Washington: US Vice President Joe Biden has urged Ukrainian President Petro Poroshenko "do his part to avoid escalating tensions" with Russia in the Crimean peninsula, the White House said. Speaking over phone, Biden on Friday assured Poroshenko that the US had urged Russia to do the same, EFE news reported. "Both leaders reiterated their strong support for political and diplomatic means to restore Ukraine's sovereignty and territorial integrity," said the statement. It also said Crimea was "occupied" by Russia "in contravention of international law". On Wednesday, Russian President Vladimir Putin said Ukrainian military intelligence units had tried to infiltrate into Crimea on two sabotage missions against critical infrastructure in the peninsula. Poroshenko, for his part, ordered on Thursday troops on maximum alert along the line separating them and the rebel forces in Crimea, and claimed the Russian accusations were a pretext for launching fresh military threats. Biden and Poroshenko also reviewed Ukraine's "recent progress" in complying with the International Monetary Fund's conditions for the next credit tranche.