VILNIUS (Reuters) - Russia has suspended a 2001 agreement on mutual military inspections with Lithuania, the defense ministry said on Monday, amid growing worries in the Baltic region over Moscow's assertiveness in Ukraine.

Under their agreement, Lithuania could inspect forces in Kaliningrad, a Russian exclave between Lithuania and Poland that is the headquarters of the Russian Baltic fleet, while Russia could do likewise with the Lithuanian military.

"Lithuania kept all conditions of this agreement and has not given a pretext for such Russian action," a spokesperson for Lithuania's defense ministry said in an e-mail to Reuters.

The three Baltic states of Estonia, Latvia and Lithuania, all former Soviet republics with small military forces, have been warily watching Russia reasserting itself in its former dominions further south.

A total of 600 U.S. troops have now been deployed to Poland and the Baltics for infantry exercises, where they are expected to remain on rotation until the end of the year.

Last week, four British Royal Air Force Typhoon fighter jets also arrived in Lithuania, the first of 12 fighters that will boost air patrols in the Baltics.

(Reporting by Andrius Sytas; Editing by Tom Heneghan)