Kiev, Ukraine (CNN) -- Foreign ministers from around the world didn't strike a deal over the Ukraine crisis Wednesday, but U.S. Secretary of State John Kerry said they agreed on one key thing: They'd rather talk than fight.
"All parties agreed today that it is important to try to resolve these issues through dialogue," Kerry told reporters after a series of meetings in Paris with foreign ministers from the United Kingdom, France, Germany, Ukraine and Russia.
Kerry described the talks as "the beginning of a negotiation" and called them "very constructive." Finding a resolution will be difficult, he said, "but I'd rather be where we are today than where we were yesterday."
French Foreign Minister Laurent Fabius offered an optimistic assessment.
"For the first time, something has moved in the process," he said, "and we will continue to talk."
Meanwhile, Russia's foreign ministry said in a statement that an agreement with the United States had been reached to help implement a February 21 deal over the transition of power in Ukraine. But Kerry did not mention that agreement in his remarks.
The closely watched talks among top diplomats came after days of simmering tensions in Ukraine's Crimean peninsula.
Ukrainian officials and Western diplomats accuse Russia of sending thousands of troops into the region in the past week -- a claim Russia has denied, while maintaining that it has the right to use military force there if necessary to protect ethnic Russians.
But what if diplomacy fails? Interim Ukrainian Prime Minister Arseniy Yatsenyuk told CNN Wednesday that he's worried about that possibility.
Yatsenyuk told CNN's Matthew Chance that he'd spoken directly with Russian Prime Minister Dmitry Medvedev and called for a diplomatic solution.
"We have just two options on the table. The first one is a political option, and the other one is military," Yatsenyuk said. "I believe that the right one is to use all diplomatic and political tools to tackle the crisis and to stop the invasion."
Military force, he said, "is the way to nowhere."
Kerry said Wednesday that it's up to Russia "to choose to de-escalate the situation" by sending troops back to their barracks and welcoming "international observers and human rights monitors" into the peninsula.
The United States' position on the crisis has not changed, he said.
"Russia's violation of Ukraine's sovereignty and territorial integrity has actually united the world in support of the Ukrainian people," Kerry said.
Fears of instability
As talks continued, tensions ran high in parts of Crimea.
Robert Serry, the U.N. envoy to Ukraine, said he was threatened by unidentified armed men in the port city of Sevastopol who tried to force him into a car.
For hours, he said he was holed up in a cafe as protesters swarmed the area. Eventually, he was escorted safely to the airport and left the country.
Speaking to CNN's Wolf Blitzer via phone from Istanbul, Serry said his experience shows how terrible tensions have become.
"What has happened to me, I hope serves as a reminder to all, how dangerous the situation has become in the Crimea," he said. "There is a very urgent need to de-escalate the situation. All those who are responsible, who can do that must have cool heads, lower their rhetoric and address this situation."
Leaders, he said, must do whatever they can to calm tensions.
"There is a lot of mistrust," he said. "That can only be overcome if we find a mechanism now for all these people to start talking."
In the eastern Ukrainian city of Donetsk, protesters took over a local government building and were seen heading to the local treasury, witnesses told CNN Wednesday.
The protesters were calling for a referendum on the status of the Donetsk region and said they want to see the region gain more autonomy.
Sergey Aksyonov, the newly installed pro-Russian Prime Minister of Crimea, told CNN's Diana Magnay Wednesday that the descriptions of the realities on the ground had been overblown. Troops in the region, he said, are legal self-defense forces.
"I think somebody is just overestimating the situation," he said. "People of Crimea are controlling the situation themselves."
Some Russian troops could end up among them, he said, but that shouldn't be cause for alarm.
"Today in almost all of our cities, there is an active military selection to the future army of Autonomous Republic of Crimea. So it is not excluded that there may be some Russian military personnel that theoretically could sign up," he said. "We are not checking passports and don't know where all the people there belong to."
While tensions were high near military bases, calm daily life continued in much of the peninsula, CNN's Ben Wedeman reported.
"It's not a situation of chaos or disorder," he said. "In fact, outside of those areas around military bases, it's amazing how normal life appears to be."
Andriy Parubiy, secretary of Ukraine's Security and Defense Council, told reporters in Kiev on Wednesday that the situation in Crimea was calmer than it had been Tuesday.
Parubiy said Russian forces had made no new military gains on the peninsula but warned of the danger of new attempts by pro-Russian protesters to take over government buildings in eastern and southern Ukraine.
Several U.S. officials said that though those Russian forces had, for the most part, not returned to their barracks, they saw no major strategic movements by them on either side of the border -- for the second consecutive day.
No meeting between foreign ministers of Russia, Ukraine
Kerry and his Russian counterpart, Sergey Lavrov, met three times Wednesday in Paris. They greeted each other cordially during one session at the Russian Embassy, according to the pool reporter traveling with Kerry.
Kerry urged direct talks between Russia and Ukraine to resolve the crisis, the official said.
"We are all concerned at what is happening there (Ukraine)," Lavrov told reporters. "We agreed to continue those discussions in the days to come to see how best we can help stabilize normalize the situation and overcome the crisis."
By day's end, Lavrov had not met with his Ukrainian counterpart, Andrii Deshchytsia.
In a joint statement after meeting Wednesday, the United States, the United Kingdom and Ukraine called for international observers to be deployed to Ukraine.
This, they said, "would help address any concerns regarding irregular forces, military activity and the treatment of all Ukrainians irrespective of their ethnicity or spoken language."
NATO reviews Russia relationship
Earlier Wednesday, NATO warned it was reviewing its relationship with Russia and threats of sanctions -- and retaliations -- flew between Europe and Russia.
At NATO headquarters in Brussels, Belgium, Secretary General Anders Fogh Rasmussen told reporters that the international body had decided to "put the entire range of NATO-Russia cooperation under review" to send "a clear message Russia's actions have consequences."
Planning for the first NATO-Russia joint mission -- the maritime escort of a U.S. ship involved in neutralizing chemical weapons -- has been suspended, though the decision will not affect the destruction of chemical weapons, he said.
And no staff-level civilian or military meetings with Russia will take place "for now," Rasmussen said.
In addition, he said, the organization will "intensify" its partnership with Ukraine, stepping up engagement with its civilian and military leadership through increased joint training and exercises and doing more to include Ukraine in multinational projects.
Russia's ambassador to NATO criticized the secretary general's statement, saying it was made before his country had a chance to present its side.
"We are very much disappointed by the outcome of the meeting we had today. The Russia delegation arrived assuming that we are going to have discussions to exchange our points of view," Ambassador Alexander Grushko said.
"This meeting proved that NATO still has a double-standards policy, and still Cold War stereotypes are applied to the Russian Federation," Grushko said.
After the meeting, a NATO diplomat said there had been tense moments as Russian representatives skirted questions about practical steps that could be taken to de-escalate the situation in Ukraine.
"There were was nothing from the Cold War atmosphere that we hear mentioned a lot by Russian officials. It was actually a frank discussion, as we should have in these sorts of meetings," the NATO diplomat said, "because this is a very serious situation where security in Europe is at stake and the basic principals of international relations are at stake and Russia is in clear breach of those."
Possibility of sanctions
Russia has been warned that possible sanctions will be on the agenda when European Union leaders meet Thursday in Brussels if no progress is made in ending the showdown sparked by Russia's military intervention in Ukraine's Crimea region.
The impact of sanctions, if they were imposed, might be felt by other countries, too. In a tit-for-tat move, Russian lawmakers are drafting a law that would allow Russia to confiscate assets belonging to U.S. and European companies if sanctions are slapped on Moscow, Russian state media reported.
The Russian threat was not specific, but numerous large European and U.S. companies have interests in the region, and Russia is a major supplier of gas to Europe
Germany's support for sanctions against Russia could be a key bargaining chip as talks go forward, said Bill Richardson, former U.S. Ambassador to the United Nations.
"They're the strongest economic country in Europe, and they're the country with the most natural gas energy ties to Russia. So if they start slipping away, and not joining the sanctions and the pressure, then Russia is almost home free," Richardson told CNN's "AC360."
For Western countries interested in turning the tide in Ukraine, Richardson said, the key now is sticking to their guns.
"Put the pressure on Putin that the sanctions are going to happen, that there's going to be diplomatic isolation," Richardson said. "Otherwise he's going to call our bluff and be more aggressive."
CNN's Michael Holmes reported in Kiev, Laura Smith-Spark wrote and contributed in London and Catherine E. Shoichet wrote and contributed in Atlanta. CNN's Pete Burn, Greg Botelho, Susannah Palk, Anna Coren, Tom Watkins, Elise Labott, Richard Roth, Khushbu Shah, Neda Farshbaf, Damien Ward, Carol Jordan and Larry Register contributed to this report.