The Baltic states will formally ask NATO to deploy several thousand troops as a deterrent, Lithuania said Thursday, amid tensions with Russia over the conflict in eastern Ukraine.

"We are seeking a brigade-size unit so that every Baltic nation would have a battalion," military spokesman Captain Mindaugas Neimontas told AFP.

He said Lithuanian, Latvian and Estonian generals would soon send a joint request to U.S. Gen. Philip Breedlove, NATO's top commander.

He said the Baltic states were to seek "permanent rotational NATO forces" as a "deterrence measure given the security situation in the region."

He refused to elaborate on specific numbers but a standard brigade could have around 3,000 troops.

Since last year, the United States has deployed around 600 troops in the Baltic states and Poland on rotational basis.

But some European NATO allies, like Germany, have been skeptical about a substantial permanent deployment, saying it could breach a 1997 agreement between NATO and Russia.

Some NATO diplomats also say the alliance is focusing on new "spearhead force" which could be rapidly deployed to deal crises both in the South or East, rather than new permanent deployments.

The Baltic republics were under Soviet rule from the end of World War II to 1991. They now fear Moscow could try to destabilize them to test NATO's commitment to collective defense.