The Biden administration comments come as Ukraine is urging an accelerated entry into NATO.
Russia still has about 100,000 soldiers deployed near its western border with Ukraine and in annexed Crimea despite Moscow announcing a military pullback last month amid soaring tensions with Kyiv, the head of Ukraine’s state security service has said.
Ivan Bakanov’s comments on Tuesday echoed earlier remarks by Ukraine’s President Volodymyr Zelenskyy, who on Monday accused Russia of having failed to fully withdraw military hardware and troops from the border areas following the two countries’ standoff.
Russia’s military build-up took place against the backdrop of an uptick in fighting in Ukraine’s conflict-stricken eastern regions of Donetsk and Luhansk, where government forces have battled Russian-backed separatist forces since the rebels seized a swath of territory there in April 2014.
As part of Moscow’s manoeuvres, Russian military units also conducted exercises in the Black Sea region of Crimea, which was seized from Kyiv in March 2014.
Russia did not publicly declare the number of soldiers it had moved to the border areas, but the European Union’s top diplomat Josep Borrell in mid-April put the figure at more than 100,000.
NATO and the United States – the leading member of the transatlantic security alliance – meanwhile said the build-up was Russia’s largest since it undertook the annexation of Crimea.
Moscow defended the troop movements, saying they were part of a training exercise called in response to activity by NATO and Ukraine, which is an ally of the group but not a formal member.
After weeks of simmering tensions, it ordered a withdrawal of some troops beginning April 23.
But the crisis has sent Russia’s relations with Kyiv and its Western allies plunging to new lows, with ties also strained over Moscow’s treatment of jailed Kremlin critic Alexey Navalny, and accusations of hacking and election interference.
US Secretary of State Antony Blinken last week said Washington could increase security assistance for Ukraine after what he called Russia’s “reckless and aggressive” actions in massing troops near the Ukrainian border.
During a visit to Kyiv, Blinken said Russia had left behind significant quantities of soldiers and equipment despite announcing the withdrawal of its forces from the area.
Blinken also said US President Joe Biden was keen to visit Ukraine and meet Zelenskyy, but gave no details on that, or on Washington’s view of Ukraine’s aspirations to join the NATO military alliance.
Zelenskyy said at the time that Russia had withdrawn only about 3,500 of the tens of thousands of troops deployed to the Crimean Peninsula.
Washington has been Kyiv’s most powerful backer since Russia annexed Crimea and the conflict in eastern Ukraine began. Kyiv says the fighting has killed 14,000 people in seven years.