Mariupol, Ukraine (CNN) -- A top European Union official said Saturday that new sanctions will be proposed within a week against Russia over its actions in Ukraine, but Ukrainian President Petro Poroshenko sounded like he can't wait that long.
"I think we are very close to the point of no return," Poroshenko said Saturday following an EU summit in Brussels. "The point of no return is full-scale war, which already happened in the territory controlled by separatists and where -- instead of separatists -- there are regular Russian troops."
Poroshenko said the situation had worsened in the last few days and that thousands of foreign troops and hundreds of foreign tanks are now on Ukrainian territory.
Russia has repeatedly denied either supporting the rebels or sending its own troops over the border. But those assertions have been roundly rejected by the West.
European Council President Herman Van Rompuy, speaking at the summit, said new sanctions will be proposed.
"The European Council says that it stands ready to take further significant steps in the light of the evolution of the situation on the ground and it requests the commission to urgently undertake preparatory work ... and present proposals for consideration within a week," Rompuy said.
Russian President Vladimir Putin appeared defiant in the face of a chorus of Western condemnation over what NATO says is clear evidence of Russian military aggression in Ukraine.
Moscow doesn't want or intend to wade into any "large-scale conflicts," Putin said Friday at a youth forum, state-run Itar-Tass reported. A few breaths later, he made the point that Russia is "strengthening our nuclear deterrence forces and our armed forces," making them more efficient and modernized.
"I want to remind you that Russia is one of the most powerful nuclear nations," the President said. "This is a reality, not just words."
German Chancellor Angela Merkel and U.S. President Barack Obama agreed in a phone call Thursday that they would have to consider tougher action against Russia.
The European Union and the United States have already slapped economic sanctions on targeted Russian individuals and businesses. The union also has sanctioned certain sectors of the Russian economy, prompting Russia to retaliate with its own measures.
Port city fortifies
The Ukrainian military worked to fortify the port city of Mariupol after Russian intelligence groups were observed there, Col. Andriy Lysenko, spokesman for the Ukrainian National Defense and Security Council, said Saturday.
A CNN team saw Ukrainian forces strengthening defensive positions on the eastern outskirts of the city, reinforcing checkpoints and digging trenches along roads leading toward the Russian border.
Beyond these checkpoints, the team found a small advance detachment of Ukrainian troops on the main road about halfway between Mariupol and Novoazovsk. The soldiers said it had been quiet Saturday.
The CNN team encountered the first pro-Russian rebel roadblock a short distance outside Novoazovsk, about 12 miles (20 kilometers) from the Russian border, with concrete blocks across the road and a heavy machine gun among the weaponry.
A 12.7 mm heavy machine gun was among the weapons at the roadblock. The fighters would not allow the CNN team to pass through but said they should "come back tomorrow."
There is a large stretch of territory east of Mariupol, some 15-30 kilometers wide depending on location, that is occupied by neither Ukrainian forces nor pro-Russian fighters.
In the villages between the two "front lines" there are no signs of damage. Some stores are open and there is some civilian traffic on the roads. Long queues have formed at one checkpoint out of Mariupol as people from rural areas try to get in and out of the city.
Denials 'without credibility'
Russia annexed Ukraine's Crimean peninsula in March, following the ouster of pro-Moscow President Viktor Yanukovych the previous month.
Violence broke out in the eastern Donetsk and Luhansk regions in April, as separatist leaders declared independence from the government in Kiev. Since mid-April, the conflict between the pro-Russia rebels and the Ukrainian military has cost more than 2,500 lives, according to the United Nations.
White House spokesman Josh Earnest said Friday that -- whatever the Kremlin says -- the reality is Russian troops are inside Ukraine and have fired on Ukrainian military positions.
In response, Foreign Minister Sergey Lavrov said NATO had previously used "images from computer games" to -- in his view -- falsely make the case that Russian troops are in Ukraine, and said the "latest accusations are pretty similar."
CNN's Tim Lister reported from Mariupol and Laura Smith-Spark wrote and reported in London. CNN's Lindsay Isaac, Max Foster, Alla Eshchenko, Barbara Starr and Greg Botelho contributed to this report, as did journalist Victoria Butenko in Kiev.