INTERNATIONAL: U.S. President Joe Biden and his Russian counterpart Vladimir Putin will speak on Saturday as Western nations warned a war in Ukraine could ignite at any moment.

Putin requested the telephone call between the leaders to take place on Monday, a White House official said, but Biden wanted to conduct it sooner as Washington detailed increasingly vivid accounts of a possible attack on Ukraine.

U.S. Secretary of State Antony Blinken expressed hope that Putin would choose diplomacy but said Washington would impose swift economic sanctions if Moscow invades.

Moscow has repeatedly disputed Washington's version of events, saying it has massed more than 100,000 troops near the Ukrainian border to maintain its security against aggression by NATO allies.

Australia and New Zealand on Saturday joined the countries urging their citizens to leave Ukraine, after Washington said a Russian invasion, including a possible air assault, could occur anytime.

Putin, jostling for influence in post-Cold War Europe, is seeking security guarantees from Biden to block Kyiv's entry into NATO and missile deployments near Russia's borders.

Still, Biden, who will join the weekend call from the mountainside presidential retreat in Camp David, Maryland, has long believed that one-on-one engagement with Putin may be the best chance at a resolution.

Two calls in December between Biden and Putin produced no breakthroughs but set the stage for diplomacy between their aides. The two leaders have not spoken since, and diplomats from both sides have struggled to find common ground. Four-way talks in Berlin between Russia, Ukraine, Germany and France on Thursday made no progress.

Putin also plans to speak with French President Emmanuel Macron on Saturday, according to Russia's TASS news agency.