Five NATO ships arrived Friday in Lithuania's port of Klaipeda to bolster defence in the Baltic region amid tensions with Russia over Ukraine, the country's defence ministry said.

At a ceremony in Klaipeda, Lithuanian Defence Minister Juozas Olekas welcomed the ships -- four minesweepers and a support vessel from Norway, the Netherlands, Belgium and Estonia -- as NATO seeks to reassure jittery member states.

"The arrival of NATO ships is yet another sign of NATO unity and solidarity," Olekas told AFP by phone after the ceremony in the western port city.

He called NATO's increased presence a "deterrence measure" against Russia, which has an estimated 40,000 troops massed on Ukraine's eastern border.

NATO deployed the naval group to the Baltic Sea last week, saying it was a sign of "the alliance's commitment to the safety and security of the Baltic member states".

Lithuania's defence ministry said the NATO ships would also visit other Baltic ports and participate in a mine-hunting operation in neighbouring Latvia later this month.

About 600 US troops have been sent to Lithuania, Latvia, Estonia and Poland in recent weeks, while Britain, Denmark and France have sent extra fighter jets.

On Friday, British Defence Minister Philip Hammond visited his troops at Lithuania's Siauliai air base, after a first stop in Estonia where Britain sent 90 troops for military drills.

"This is a reaffirmation of our commitment to NATO and a reminder that NATO is based on a commitment by each member state to the others to come to their aid," Hammond told reporters in front one of the four British Typhoons deployed to Lithuania.

He added that NATO will "keep under review" its presence in Eastern Europe but insisted that the alliance will do so by "not crossing the line into provocation".

Russian actions in Ukraine have rattled nerves in the Baltic states, which were occupied and annexed by Moscow during World War II.

The three countries -- Lithuania, Latvia and Estonia -- broke free from the crumbling Soviet Union in 1991 and joined both the European Union and NATO in 2004.