BRUSSELS, Jan 12 - Russia has not committed to de-escalate on the Ukrainian border after two rounds of diplomatic talks this week, Deputy US Secretary of State Wendy Sherman said Wednesday, CNN reported.

The US also acknowledged it's still unclear whether Moscow intends to use the talks this week as a pretext to claim that diplomacy cannot work.

Sherman told reporters that Wednesday's meeting between NATO and Russia ended with a "sober challenge from the NATO allies to Russia" to respond to the opportunities offered by the international community to de-escalate the situation on the border with Ukraine and choose the path of diplomacy.

But Sherman, who spoke forcefully about the West's unified message to Moscow following the roughly four-hour session in Brussels, made clear the US and its Western allies don't yet know what Russian President Vladimir Putin's aims are following the diplomatic meetings, with more than 100,000 Russian troops positioned on the Ukrainian border.

In statements Wednesday, Russian officials suggested Moscow could resort to military action if political efforts fail. That warning came a day after the Russian military conducted live-fire exercises along the border.

As the talks this week, the US has finalized sanctions options in the event that Russia invades Ukraine, senior administration officials said on Wednesday.

"When live fire exercises are reported this morning. What is this about?" Sherman said, referring to reports about Russian exercises. "Is this about invasion? Is this about intimidation? Is this about trying to be subversive? I don't know. But it is not conducive to getting diplomatic solutions."

Asked by CNN's Alex Marquardt if the Russians had made any commitments to de-escalate, Sherman said they did not.

"There was no commitment to de-escalation, no," she said, before pausing and adding: "Nor was there a statement that there would not be."

Sherman suggested that the Russians themselves may not even know how they intend to use or act upon this week's diplomatic talks with the US and NATO. She said that the US believes that progress can be made -- if Russia engages on issues where there are overlapping interests.

"There is plenty to work on, where we have places where we can enhance mutual security. There are some places we cannot. But there is progress that can be made," Sherman said.

Sherman told CNN's Christianne Amanpour later Wednesday that she believed Putin amassed troops on the border of Ukraine in order to "put pressure on Europe and the United States, to put pressure on the euro Atlantic ambition, to... intimidate, to coerce, and to say 'I've got sticks I can bring to this discussion' as well."

Following Wednesday's meetings, Russian Deputy Foreign Minister Alexander Grushko warned that Moscow would resort to military measures if the political course fails to fend off threats to its security, according to Russian state media RIA Novosti.

"We have a set of legal military-technical measures that we will apply if we feel a real threat to (our) security, and we already feel (it), if our territory is considered as an object for targeted strike weapons," Grushko told reporters, according to Russian state media. "Of course, we cannot agree with this. We will take all necessary measures to fend off the threat by military means if it does not work out with political means."

Russia's deputy defense minister Alexander Fomin also issued a statement Wednesday sounding pessimistic about the talks, saying it was NATO who was ignoring Russia's proposals to de-escalate -- and warning that could lead to conflicts.

"The Russian side has repeatedly proposed to the alliance to take measures to de-escalate the situation," Fomin said. "On the part of the alliance, Russian initiatives were ignored. This creates prerequisites for incidents and conflicts, undermines the foundations of security."

During Wednesday's roughly meeting -- which went longer than scheduled -- Sherman said that the US and its NATO allies once again made clear Russia's demand Ukraine never be permitted to join NATO was a non-starter. Sherman called it "hard to understand" how Russia could feel threatened by Ukraine when it has the largest conventional military in Europe.

Wednesday's session with the NATO-Russia Council was the second of three planned for this week. The US delegation led by Sherman met with the Russians on Monday, and the Organization for Security and Cooperation in Europe will hold a session with Russia on Thursday in Vienna. (om/ez)