VIENNA/MOSCOW, Jan 13 (Reuters) - Poland's foreign minister said on Thursday that Europe was at risk of plunging into war as Russia said it was not yet giving up on diplomacy but that military experts were preparing options in case tensions over Ukraine could not be defused.

In Washington, the White House said the threat of a Russian invasion of Ukraine remained high with some 100,000 Russian troops deployed and the United States would make public within 24 hours intelligence suggesting Russia might seek to invent a pretext to justify one.

"The drumbeat of war is sounding loud, and the rhetoric has gotten rather shrill," Michael Carpenter, U.S. Ambassador to the Organization for Security and Cooperation in Europe (OSCE), said after talks with Russia in Vienna.

"The threat of military invasion is high," White House national security adviser Jake Sullivan told reporters. "There are no dates set for any more talks. We have to consult with allies and partners first."

Russia said dialogue was continuing but was hitting a dead end as it tried to persuade the West to bar Ukraine from joining NATO and roll back decades of alliance expansion in Europe - demands that the United States has called "non-starters".

"At this stage it is really disappointing," Russian Ambassador Alexander Lukashevich told reporters after a meeting of the OSCE, the third leg in a series of East-West talks this week.

He warned of possible "catastrophic consequences" if the two sides could not agree on what Russia has termed security red lines but said Moscow had not given up on diplomacy and would even speed it up.

The Russian comments reflect a pattern of Moscow saying it wants to pursue diplomacy but rejecting calls to reverse its troop build-up near Ukraine and warning of unspecified consequences for Western security if its demands go unheeded.

Earlier, Polish Foreign Minister Zbigniew Rau told the 57-nation security forum: "It seems that the risk of war in the OSCE area is now greater than ever before in the last 30 years."

While overlooking wars during that period in the former Yugoslavia and parts of the former Soviet Union, his comment highlighted the level of European anxiety over Russia's build-up of some 100,000 troops within reach of its border with Ukraine.

Russia denies plans to invade Ukraine but its military build-up has forced the United States and its allies to the negotiating table.

Rau reported no breakthrough at the Vienna meeting, which followed Russia-U.S. talks in Geneva on Monday and a Russia-NATO conference in Brussels on Wednesday.