NATO on Wednesday expressed alarm over a "wide-ranging" military build-up by Russia in Crimea, as well as talk that Moscow could even install nuclear weapons on the annexed Black Sea peninsula.

A statement issued during two days of talks by the military alliance's top diplomats, in the Turkish resort of Antalya, said "we do not and will not" recognise Russia's 2014 annexation of Crimea from Ukraine.

"We condemn Russia's ongoing and wide-ranging military build-up in Crimea and are concerned by Russia's efforts and stated plans for a further military build up in the Black Sea region," it added.

The statement warned this risked having "further implications" for stability in the region.

It also expressed alarm over "statements by the Russian leadership" about the possible stationing of nuclear weapons in Crimea.

NATO Secretary General Jens Stoltenberg added: "We are deeply concerned by statements of possible future stationing of nuclear weapons and development systems in Crimea."

A NATO source told AFP that such statements had been repeatedly made by Russian officials since March.

In March, Russian foreign ministry official Mikhail Ulyanov, who heads the ministry's non-proliferation department, did not rule out Russia stationing nuclear weapons in Crimea.

"Russia surely has the right to station nuclear weapons on its territory, if it considers it necessary, in any region," he said.

Ukrainian Foreign Minister Pavlo Klimkin said it was illegal for Russia to so much as evoke the possibility of stationing nuclear weapons on Crimea.

"The messages from the Russian side about the sheer possibility is a complete breach of international obligations," he said.

On the future of Crimea, Klimkin said: "Crimea was Ukrainian, is Ukrainian and will be Ukrainian."

The NATO-Ukraine Commission also slammed the "worsening rights situation" in Crimea under Russian rule, in particular the treatment of the Crimean Tatar Turkic minority.

Russia annexed Crimea in 2014 in a move that was widely condemned by the international community but was greeted as a great patriotic victory at home.

NATO also warned President Vladimir Putin to waste no time in implementing a fragile peace deal to end the fighting in eastern Ukraine, after the Russian strongman's meeting with US Secretary of State John Kerry on Tuesday raised hopes of a slackening in tensions.