London (AFP) - NATO should beef up its maritime arm in response to the rising threat from an increasingly "bold" and "aggressive" Russia, commanders said on Wednesday.

The 28-member defence alliance's naval forces have in recent years focused on issues such as counter-terrorism and piracy, but speakers at a London conference said the group needed to prepare more to counter Russian military ambitions.

"Russian international maritime presence has grown significantly in recent years, specifically since the Ukraine crisis erupted in 2014," senior NATO commander General Adrian Bradshaw, told a conference in London on NATO's naval future.

"The Russian Federation is shadowing and presumably collecting intelligence from NATO nation naval units in the Baltic, the Atlantic, the Mediterranean and the Black Sea, using methods that can be considered bold and sometimes aggressive," he said.

One area that NATO will focus on is how to better project maritime force on land using amphibious units and air power, said British Vice Admiral Peter Hudson.

"At the height of the Cold War in the 60s and 70s, the striking power of the US Navy, the delivery of large amounts of land forces to support Europe was quite a sophisticated art," he said.

"You'll see a lot of our exercises in recent years, and certainly ones that are coming up in the future, are working hard to bring that capability back."

NATO will from September to November launch its largest exercises in more than two decades, in regions including the Atlantic Ocean and the Mediterranean Sea.

"We have to reinforce their approach to high-intensity crisis," said General Jean-Paul Palomeros, a senior NATO commander, referring to NATO's maritime arm.

In a rare move, the US military released a video last month of a Russian Su-24 bomber flying past an American warship in the Black Sea, while Sweden last year launched a massive hunt for a suspected Russian submarine in the Stockholm archipelago.

Russia is upgrading its naval capabilities, and in May unveiled designs for two new major warships, a multi-purpose heavy aircraft carrier called the "Shtorm" and a new class of destroyer called the "Shkval".

Russia considers the NATO military presence in formerly Soviet-ruled central and eastern Europe is encroaching on its sphere of influence.