A plane carrying two U.S. senators was detained for several hours Sunday while trying to leave Russia, before being permitted to leave the country for Ukraine, according to spokesmen for the lawmakers.

Sens. Richard Lugar (search), R-Ind., chairman of the Senate Foreign Relations Committee, and Barack Obama (search), D-Ill., who had both been visiting storage sites for weapons of mass destruction, were held at an airport in the Ural Mountain city of Perm for several hours, but were allowed to leave after talks between U.S. and Russian officials.

"I am in Ukraine with Sen. Lugar," Lugar's spokesman, Andy Fisher, said in a message sent from a personal messaging device Sunday afternoon.

He said Russian officials refused to let the plane take off for three hours and insisted on boarding it. "They did not. The border patrol finally got orders to let us go," Fisher said.

"We were treated just fine," he said.

A spokesman for Obama also confirmed the plane's arrival in Ukraine.

The senators and their aides spent three days in Russia visiting sites where warheads are stored before destruction under the U.S.-funded Comprehensive Threat Reduction program (search).

The spokesmen did not have information on the nature of the dispute that resulted in the senators' being held. Telephone calls to the Russian border guard service and Foreign Ministry were not answered Sunday evening.