Josh Lederman

Associated Press

WARSAW, Poland – Denouncing Russia's actions in Crimea as "nothing more than a land grab," Vice President Joe Biden warned Russia on Tuesday that the U.S. and Europe will impose further sanctions as Moscow moves to annex part of Ukraine.

With limited options, the United States was seeking ways to show it wouldn't stand idly by as Russian President Vladimir Putin signed a treaty for the Ukrainian peninsula of Crimea to join Russia. So far, Putin has been undeterred by sanctions and visa bans levied by the U.S. and the European Union, and there's no U.S. appetite for military intervention.

"Russia has offered a variety of arguments to justify what is nothing more than a land grab, including what he said today," Biden said in Poland, which shares a border with both Russia and Ukraine.

Biden arrived early Tuesday in a region on edge over Russia's nascent aggression in Crimea. Amid eerie echoes of the Cold War, U.S. allies including Poland have raised concerns that they could be next should the global community be unable to persuade Putin to back down.

Former Soviet states are among the most alarmed by the prospect that Moscow could be resuming its traditional imperial ambitions. But Ukraine is at greater risk militarily because it lacks membership in NATO and the promise of collective defensive measures that NATO membership provides.

Biden said the U.S. commitment to defending its NATO allies is "ironclad." He promised more sanctions would be coming, along with new NATO training and exercises that will take place in Poland.

The vice president said the U.S. was considering rotating American forces to the Baltic region to ensure the collective defense of NATO allies. Those forces could conduct ground and naval exercises, plus engage in training missions.