Russia says its troops are pulling back. Biden says the threat of an invasion is still ‘very high.’

The United States and Russia continued to clash over the fate of Ukraine, with President Biden warning Thursday that the threat of a Russian attack remained “very high,” even as the Kremlin insisted that it was withdrawing troops from border areas and said in writing it was not planning an invasion.

But Russia repeated its threat of unspecified “military-technical measures” if the United States did not accede to its demands for sweeping changes to security arrangements in Eastern Europe, a signal that President Vladimir V. Putin would use his large-scale military buildup around Ukraine to extract concessions from Western nations determined to avert a war.