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A senior US official warned Thursday that the “drumbeat of war is sounding loud” following a week’s worth of diplomacy between the West and Russia that wrapped up Thursday.

The effort ended without clear breakthroughs over the tens of thousands of Russian troops amassed on the Ukrainian border, leaving prospects for future diplomacy and de-escalation in doubt as Russian officials suggested they could soon turn to military options.

Both US and Russian officials sounded a pessimistic note over the talks following Thursday’s meeting in Vienna at the Organization for Security and Cooperation in Europe (OSCE). It was the third session that capped a week of intensive meetings that the United States and its NATO allies hoped could spur Russia to pursue a path of “de-escalation and diplomacy” rather than mobilizing the tens of thousands of Russian troops whose presence has swelled along Ukraine’s borders.

But Russian officials reacted with frustration and impatience coming out of the meetings, suggesting they were poised to abandon discussions over the US and NATO’s refusal to entertain Moscow’s key demands: A guarantee that Ukraine will never be permitted to join NATO and that the alliance roll back its expansion in Eastern Europe. The US and its NATO allies have repeatedly said such proposals from Moscow are non-starters.

Russian Deputy Foreign Minister Sergey Ryabkov suggested the talks had reached “a dead-end or a difference in approaches” because the US and NATO would not address Moscow’s demands about Ukraine never joining NATO, he said, according to Russian state media TASS. Ryabkov said he didn’t see a reason for the two sides to continue talks, even though the US has suggested they would continue beyond this week.

Following Thursday’s session, the US Ambassador to the OSCE Michael Carpenter told reporters that the “drumbeat of war is sounding loud and the rhetoric has gotten rather shrill”

“We have to take this very seriously,” Carpenter said of the massing of Russian troops along the border with Ukraine. “We have to prepare for the eventuality that there could be an escalation.”

Polish Foreign Minister Zbigniew Rau, the OSCE chairman, warned after Thursday’s meeting that the “risk of war in the OSCE area is now greater than ever before in the last 30 years.”

The diplomatic efforts this week – which included separate sessions between Russia and the US, NATO and the OSCE – were aimed at pulling back Russia from a potential invasion of Ukraine. But Russia did not commit to pulling back the more than 100,000 troops now along the border, and the Russian military conducted live-fire exercises along the border this week as the talks were ongoing.

‘The jury’s out on which path Vladimir Putin is going to choose’

US officials made clear heading into the talks they did not know whether Russia was serious about diplomacy or just planned to use the sessions as a pretext for military action.

“The jury’s out on which path Vladimir Putin is going to choose,” Secretary of State Antony Blinken said Thursday in an interview with MSNBC. “Is he going to choose the path of diplomacy and dialogue to resolve some of these problems or is he going to pursue confrontation and aggression?”

National Security adviser Jake Sullivan told reporters at the White House Thursday that the US and its allies remain prepared for any outcome following this week’s talks.

“The discussions were frank and direct. They were useful. They gave us and our allies things to consider; they gave Russia things to consider,” Sullivan said. “We will now reflect and consult with allies and partners on how to proceed,” Sullivan told reporters at the White House.

Sullivan said that the Biden administration planned to share information soon about Russian disinformation operations that could lay the groundwork for a pretext to invade Ukraine. “Our intelligence community has developed information, which has now been downgraded, that Russia is laying the groundwork to have the option of fabricating the pretext for an invasion,” Sullivan said.

A senior US official said that in the last several days Russia has “continued to add capacity” near the border. The official said that it wasn’t a “substantial” number of troops or equipment, but it’s a signal that Kremlin is not de-escalating.

Russia’s next move still unclear

It’s still unclear what the US plans to do if Russia doesn’t de-escalate but also doesn’t invade Ukraine. Throughout the week, US officials have said Russia will face consequences like they have never seen if an invasion happens. But the Biden administration is not planning to impose any costs on Russia as a deterrent.

A senior State Department official said there is nothing that would change that approach.

“I don’t think there’s any desire to impose sanctions or consequences in advance of Russian action on the ground. I don’t think that would be a productive way to go,” the official told CNN. “I think we maintain leverage if we reserve the right to impose those consequences in the aftermath of an escalation.”

The head of the US delegation, Deputy Secretary of State Wendy Sherman, told reporters after the talks at NATO that the Russians themselves may not know yet what their next move is. Throughout this week’s talks, the US has repeatedly argued that diplomacy can’t happen unless Russia de-escalates, which Sherman on Monday said the US defined as Russia returning its troops to barracks or telling the US “that exercises are ongoing and what their purpose is.”

After Wednesday’s meeting at NATO, Sherman said Russia had not committed to any de-escalation.

Top Biden administration officials have made clear that they expect talk to continue in the near future, without providing details for what those talks might look like.

“We would expect to have additional engagement with the Russian Federation in the coming days. We hope that engagement takes place, we hope this diplomatic track continues, but even more importantly, we hope it bears fruit,” State Department Spokesperson Ned Price said on Wednesday.

Russia says US demands are ‘unacceptable’

Russia’s Foreign Minister Sergei Lavrov responded Thursday that the US demands were “unacceptable.”

“I do not think we need to explain how absolutely unacceptable such demands are, and, of course, we will not even discuss them,” Lavrov said.

US officials have expressed hope that discussions over areas of mutual interest between Russia and the US – including nuclear weapons, intermediate range missiles and transparency over military exercises – could keep the diplomatic conversations going. NATO leaders noted that Wednesday was the first time Russia had agreed to a meeting with the alliance in two years and they sat through the four hour-long meeting, which was longer than had been scheduled.

“I think the reality is that I will say that the Russian delegation sat through nearly four hours of a meeting where 30 nations spoke, and they did, which is not an easy thing to do,” she said Wednesday.

But if that gave the impression Russia might have been open to compromise positions, Russia quickly poured cold water on it.

“The US and its NATO allies are not ready to meet Russia halfway on the key issues,” Ryabkov said Thursday, according to state news agency TASS. “The main problem is that the United States and its NATO allies, under no guise, for any reason are not ready to meet our key demands.”

Blinken had warned before the talks that no breakthroughs were expected this week “in an atmosphere of escalation with a gun to Ukraine’s head.”

As Russia and NATO appeared to talk past each other, the language they used illustrated how far apart they remain. Russia had proposed specific treaty language in the weeks ahead of the meetings and called them “negotiations,” while Sherman countered that no formal terms were put forward in what she described as “discussions.”

Sherman said earlier in the week that she did not know if the Russians had come to the table for the three days of talks in good faith, or as a pretext in an attempt to justify future military action.

“If Russia walks away, however, it will be quite apparent they were never serious about pursuing diplomacy at all,” she said. “That is why collectively we are preparing for every eventuality.”

CNN’s Anna Chernova, Zahra Ullah, Mick Krever, Barbara Starr and Sam Fossum contributed to this report.