British PM warns of potential 'sheer cost in human life'; Zelensky proposes meeting with Russia leader; Putin, Macron to speak; Germany, Austria tell citizens to leave Ukraine

Kyiv approached US officials last year in bid to buy system, with Israel reportedly vetoing the prospect of a deal

Biden, Boris Johnson say there's still 'a crucial window for diplomacy' in Ukraine crisis; Russia said to move some forces to 'attack positions'

US warns that, with over 130,000 Russian troops deployed on former Soviet republic's border, backed by various missiles and tanks, major attack could be launched at any moment

Washington says it is bracing for the worst, urges all Americans to leave the country within 48 hours

Soldiers will join 1,700 American servicemen already in Poland; Biden's national security adviser warns Putin could give order to attack at any moment

US official says 2,000 soldiers from Fort Bragg, North Carolina, will be sent to Poland; roughly 1,000 Germany-based personnel to be moved to Romania

As lawmakers mull type and timing of penalties, Washington's UN envoy says Moscow to be pressed hard during Security Council meeting on Monday

White House denies comments, says president only spoke of 'a distinct possibility that the Russians could invade Ukraine in February;' US refers Ukraine crisis to Security Council

Pileup of difficult moments presents challenge to twin pillars of Biden’s candidacy -- that he could get things done competently at home and restore America’s standing abroad