Stepping into a region on edge, Vice President Joe Biden came to Poland on Tuesday to reassure anxious allies that the U.S. will stand up to Russia’s aggression in neighboring Ukraine, even as Moscow brushes aside sanctions and stern warnings from the West.

Biden arrived in Warsaw on Tuesday morning for consultations with Polish Prime Minister Donald Tusk and President Bronislaw Komorowski, a few hours after Russian President Vladimir Putin approved a draft bill for the annexation of Crimea, one of a flurry of steps to formally take over the Black Sea peninsula. Crimea on Sunday voted overwhelmingly to secede from Ukraine and try to join Russia.

On Monday, the U.S. and the European Union levied the toughest sanctions on Russia since the Cold War.

In further meetings in the Polish capital and later in Lithuania’s capital, Vilnius, Biden was to discuss the crisis with the leaders of Estonia, Lithuania and Latvia _ three Baltic nations that are deeply concerned about what Russia’s military intervention in Ukraine’s Crimean Peninsula might portend for the region. All four countries share borders with Russia; Poland also borders Ukraine.

Biden’s two-day trip is part of a broader U.S. campaign to step up pressure on Putin after Sunday’s referendum, dismissed by the U.S. as illegal. In coordination with Europe, the Obama administration has frozen the U.S. assets of nearly a dozen Russian and Ukrainian officials, although critics contend that amounts to a slap on the wrist that Moscow will blithely overlook.

In Warsaw and Vilnius, Biden will affirm the U.S. commitment to defending its NATO allies, which includes Poland and the three Baltic states but not Ukraine. A senior administration official said the vice president will discuss ways to strengthen the alliance so NATO emerges even stronger from the crisis, and will echo Obama by insisting that if Russia continues to flout international law, the costs will only increase.

Biden will also discuss what additional steps the U.S. can take to shore up security for Poland and the Baltics, such as increased training, said the official, who wasn’t authorized to comment by name and demanded anonymity.

Also on the agenda: long-term energy security in Europe, a key factor that has confounded the West’s attempts to display a united front in punishing Russia. Much of Europe is heavily dependent on Russian natural gas, and European countries have major economic interests in Russia that could be in jeopardy if Moscow retaliates with sanctions of its own.

Biden plans to address energy diversification within Europe, but will also discuss how the U.S. can help, said the official, declining to offer more details

Republican lawmakers and a handful of European countries, including Poland, have urged the White House to accelerate approval of U.S. natural gas exports to help Europe wean itself off its dependence on Russia. The White House has insisted that would take too long to help the current crisis and says Russia is too dependent on gas revenues to cut off supplies to Europe.

One option that doesn’t appear to be on the table: rethinking the U.S. posture on missile defense in the region. Poland is still bruised from Obama’s 2009 decision to cancel the final phase of a defense system sorely desired by Poland as a hedge against Russian missiles. The official said Biden will reassure Poland that the smaller, phased-in system Obama chose instead is on schedule, but won’t be discussing potential changes. (AP)