PM Tusk at Lask airbase, Monday: photo - PAP/Grzegorz Michałowski
Donald Tusk's visit to the base in central Poland comes as US and Polish air forces are carrying out joint exercises, with the United States stepping ups efforts to reassure allies in the central and eastern European region as the crisis in Ukraine continues to escalate.
Stephen Mull, US ambassador to Poland, said in March that discussions were underway on possibly expanding the scope of exercises in the future to include allies from the region such as Czech Republic, Hungary, Slovakia, Romania, Bulgaria and the Baltic states.
"Your presence in Lask gives us a greater sense of security in today's difficult times. This is very important to us," PM Tusk said in English to the US airmen and support staff at the base.
"I would like to give you a warm welcome to Poland," he said, the PAP news agency reports.
The current rotation of American airman is the second by the US since an agreement between Washington and Warsaw was made in 2011 and could last between two weeks and a month.
Meanwhile, Ukraine's acting president Oleksander Turchinov threatened military action after pro-Russian separatists occupying government buildings in the east of the country ignored an ultimatum to leave on Monday.
A Reuters journalist in the city of Slaviansk, where a gun-battle occured on Sunday, with casualties reported on both sides, has said that there is no sign of an evacuation by pro-Russian forces from the local police HQ.
In another development, at least 100 pro-Russian separatists attacked the police headquarters in the city of Horlivka on Monday.
Local Ukrainian TV has shown images of ambulance staff treating people after the attack.
The United Nations Security Council held an emergency session on Sunday night, and the United States warned that it was likely to impose further sanctions against Russia if the escalation in eastern Ukraine continues.
European Union foreign ministers were due to discuss whether to impose further sanctions on Moscow. (pg)