LONDON - Britain and Lithuania signed a joint declaration on Monday to boost defence and security collaboration, stepping up London's support of nations that fear Russian President Vladimir Putin will not stop at Ukraine in trying to redraw Europe's borders.

Since Russia invaded Ukraine on Feb. 24, Baltic states such as Lithuania, a NATO member and former Soviet state, have become increasingly concerned they could be next to face Russian aggression.

Britain said the declaration would build on the defence cooperation the countries share as NATO allies and would increase resistance to threats, including from Russia and China. It gave no further details.

"The UK and Lithuania are two countries which believe in freedom and sovereignty, and who stand up to authoritarian regimes in Europe and across the world," British foreign minister Liz Truss said in a statement.

"We stand together with Ukraine in the face of Russia’s illegal, barbaric war."

Britain has been a vocal supporter of Kyiv in its war with Russia, which Putin describes as a "special military operation" to disarm and "denazify" Ukraine. Kyiv and its Western allies say the invasion is illegal and unjustified.

(Reporting by Elizabeth Piper; Editing by Nick Macfie)