The Baltic states will formally ask NATO to deploy several thousand troops as a deterrent to Russia, Lithuania said Thursday, but the alliance gave no assurance that the request would be accepted.

NATO Secretary General Jens Stoltenberg said at meeting of the alliance's foreign ministers in the Turkish city of Antalya that he was aware such a request was being made but emphasised it was too early to assess the demand.

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

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

Neimontas 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.

Latvia's defence ministry also confirmed the move in a Thursday statement saying "the joint letter will be sent next week".

The ministry said military commanders from all three Baltic states recently decided to request a "brigade level permanent Allied military presence with a roughly battalion-level placement of units in each country."

"An Allied presence is an essential prerequisite for Latvia's security in a situation where Russia does not change its policies regarding the Ukraine conflict and at the same time strongly demonstrates its military presence and potential in the Baltic Sea region," the statement said.

In a sign of the continued tensions over Ukraine even after the Minsk truce deal, French President Francois Hollande denounced as "unacceptable" ceasefire violations in eastern Ukraine, after speaking briefly with his Ukrainian counterpart Petro Poroshenko in Germany.

"There is a risk of fresh unrest and we need to warn them of that," he said.

- 'Assess request carefully' -

Stoltenberg said he was aware a letter was going to be sent to NATO by the Baltic states.

"When we receive the letter we will go carefully through the letter and assess the proposals in that letter," he said.

"It is too early to comment on details and specifics in a letter I have not seen," he added.

But Stoltenberg emphasised that NATO had already taken decisions that would help the security of the Baltic states, such as increasing air policing and a naval presence.

"Our main focus is the implementation now of the decisions we have already made," he said.

Baltic and Nordic countries have reported an uptick in Russian military activity in the region over the last year. They claim Russian war planes are flying with their transponders switched off, endangering civil aviation.

Last month, Lithuania also accused Russian warships of thwarting work on a key underwater power link to Sweden that would reduce the Baltic state's dependence on Russian energy.

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

"If NATO fails to react positively to the request (for the troops), it can be interpreted as a certain signal," said Ramunas Vilpisauskas, director of the Institute of International Relations and Political Science in Vilnius.

"The big neighbour in the east now will now be watching closely how the biggest NATO countries will react to the letter," he told AFP, referring to Russia.

Some European NATO allies have been sceptical about a substantial permanent deployment, saying it could breach a 1997 agreement between NATO and Russia.

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

"We are constantly discussing the adaptation of the alliance," said Stoltenberg.

"We have always be able to fulfil our main responsibility which is to defend all our allies against any threat," he added.

He said the spearhead force will "make it easier to reinforce the defences of the Baltic States."

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