Russia announced Wednesday that it had begun expanding and modernising its Black Sea fleet based in Crimea with new ships and submarines, just months after annexing the peninsula from Ukraine.

"Today we have started forming a powerful Black Sea fleet with an absolutely different level of air service, coastal missile and artillery troops and marines," said Alexander Vitko, the Black Sea fleet commander, in a message to servicemen.

"We are preparing bases and crews to serve on new ships and submarines."

Vitko said the modernisation of the fleet "lays the foundation for the future of the fleet, both in the short term and looking far ahead."

Russia's Black Sea fleet had a base at the historic port city of Sevastopol in Crimea under an agreement with Ukraine before Russia annexed the peninsula in March.

President Vladimir Putin said at a meeting with the national security council Tuesday that Russia will bolster its defences to counter the creeping influence of NATO close to its borders.

"It is necessary to implement all of the country's defence measures fully and promptly, including of course in Crimea and Sevastopol, where we have to de facto create military infrastructure from scratch," he said.

Putin attended a naval parade there on May 9 Victory Day this year, when thousands crowded the harbour to watch war ships carry out manoeuvres.

Defence Minister Sergei Shoigu said in May that Russia's only warm-water fleet would get new ships and submarines this year.

Russia earlier this month announced plans to develop Sevastopol up to 2030, including building a power station to reduce its dependence on electricity from Ukraine.

It has also announced an ambitious project to build a bridge connecting Crimea to southern Russia.