"There is a threat to us all from Russia," Merz said at a press conference in Vilnius. "We are protecting ourselves against this threat -- and that is why we are here today."

The 5,000-strong heavy combat brigade, which will be built up in coming years, is aimed at bolstering NATO's eastern flank and deterring potential Russian aggression.

The deployment was prompted by Russia's 2022 invasion of Ukraine. Stationing a military unit abroad permanently is unprecedented in the post-war history of the Bundeswehr, as the German armed forces are known.

Merz, who took office this month, said the security situation on NATO's eastern fringes "remains very tense".

"Russia's aggressive revisionism threatens not only the security and territorial integrity of Ukraine -- this revisionism threatens our common security in Europe," he said.

By deploying a brigade to Lithuania and ramping up defence spending, Germany wanted to "send a clear signal to our allies" that it was "investing in our security", he added.

"Together with our partners, we are determined to defend the territory of the alliance against any aggression. The security of our Baltic allies is also our security."

Lithuania and fellow Baltic countries Estonia and Latvia, former Soviet states that have become NATO and EU members, fear they are increasingly in Moscow's crosshairs.

Germany is Ukraine's biggest military backer after the United States, and Merz emphasised that Kyiv's allies "will not allow Russia to drive a wedge between us".

"We stand firmly alongside Ukraine but we also stand together as Europeans and, whenever possible, we work as a team with the United States."

Merz said Berlin hoped "that there is a chance of reaching a ceasefire and then peace negotiations" but added that the process could take weeks or even months.

Moscow has for weeks defied Western pressure for an unconditional and immediate truce in its more than three-year offensive in Ukraine.