The US military has deployed two MQ-1 Predator surveillance drones and 70 airmen to Latvia for a two-week training mission aimed at reassuring European allies wary of Russia.

The mission, which began Friday and is due to end on September 15, comes as the United States increases military exercises and training in Eastern Europe after Russia's annexation of Crimea and repeated clashes in Ukraine between nationalists and pro-Russian separatists.

Four F-22 stealth tactical fighter aircraft have been deployed to Germany, and were used in a training exercise Monday with Polish F-16 fighter planes.

But Captain Lauren Ott, a spokeswoman for US Air Forces in Europe - Air Forces Africa, stressed that the two deployments were not connected.

The drones -- the first deployment of such unarmed, surveillance aircraft by the US military to Latvia for a training mission with allies -- will be used in Latvian air space.

They will be controlled from Lielvarde Air Base in the country, rather than from the United States.

"This temporary assignment of aircraft and personnel will test their ability to forward deploy RPA (remotely piloted aircraft) to conduct air operations," said Major James Brindle, a Pentagon spokesman.

It will also "assure our Latvian allies, NATO allies and European partners of our commitment to regional security and safety," he added.