奥巴马抵达波兰，讨论乌克兰和北约问题

U.S. President Barack Obama is in Poland on the first stop of a three-nation European tour expected to be dominated by talks on the Ukraine crisis.
 
Mr. Obama and Polish President Bronislaw Komorowski are meeting Tuesday in Warsaw after visiting with airmen from both nations who are part of a mission providing extra air support to the region following Russia's annexation of Crimea.
 
Their talks are also expected to focus on NATO and U.S.-Polish relations.
 
The two presidents will host a broader meeting later Tuesday with leaders from Central and European countries.  Mr. Obama is also scheduled to meet with Polish Prime Minister Donald Tusk.
 
The U.S. leader's trip comes as Ukraine's government battles pro-Russian separatists.  He is due to meet with Ukrainian president-elect Petro Poroshenko before leaving Poland on Wednesday.