U.S. troops sent to the Black Sea peninsula of Crimea to prepare for joint war games left Ukraine after two weeks of protests organized by pro-Russian parties prevented them from carrying out their mission.

Some 200 Marine reservists arrived in Ukraine on May 27 to help refurbish a training facility for the exercises in mid-July. But the protesters, who accused NATO and the United States of seeking a foothold in the ex-Soviet republic, prevented the reservists from getting on to the base.

The protests and continuing uncertainty over Ukraine's new government also led President Bush to put off a visit to the country this month.

U.S. and Ukrainian officials said the 200 reservists began leaving the region on Sunday because their contract had ended. Russian television broadcast footage of several dozen flag-bearing protesters shouting "Yankee Go Home!" at buses apparently carrying the Americans.

"The American reservists are departing ... because they were contracted to be here for two weeks in all and now they are going home to their families," U.S. Embassy spokesman Brent Byers said in televised comments dubbed into Russian.

"We're very disappointed that they didn't fulfill what was planned. But I want to emphasize there was no talk of founding a NATO base in the Crimea. These were only joint exercises."

Many in Ukraine, particularly in the Russian-speaking south and east, remain hostile to the United States — their former Cold War foe. Russia warned that relations between the neighbors would suffer if Ukraine joined NATO.

Opponents of President Viktor Yushchenko have been energized by his party's humiliating, third-place finish in March parliamentary elections, and the inability of the country's various parties to put together a governing coalition.

Yushchenko has made NATO membership a top priority and has been pushing for potential partners to commit to that goal in the coalition talks that have dragged on for weeks.

The United States was one of 12 nations that had been scheduled to take part in the exercises.