Russian naval activity in Europe now exceeds levels seen during the Cold War, a top US and Nato military officer has warned.

Navy Admiral Michelle Howard voiced concern the distributed nature of the deployments could end up "splitting and distracting" the transatlantic alliance.

"We're seeing activity that we didn't even see when it was the Soviet Union. It's precedential activity," the head of Nato's Allied Joint Force Command in Naples and commander of US naval forces in Europe and Africa told Reuters.

"They're a global navy, I understand that. But the activity in this theatre has substantially moved up in the last couple of years."

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Last year, Russia deployed its only aircraft carrier, the Admiral Kuznetsov, to the Syrian coast to carry out bombing missions on rebel groups and Isis as Russian President Vladimir Putin propped up Syrian President Bashar al-Assad.

Then last week, it sent its Admiral Grigorovich warship to the Syrian port of Tartus, which houses a Russian naval base.

Ms Howard said Russia had also increased patrols in the north Atlantic and Arctic region, made significant out-of-area submarine deployments, and increased submarine movement in the Black Sea.

She said there was a danger members of the Nato alliance would focus on the area of interest closest to them, while losing sight of Russian activities in other areas.

Her comments mirror those of Russian Admiral Vladimir Korolev, who told state media Russia's submarine patrols have reached a level of operation not seen since the Cold War.

Ms Howard's comments came amid a sharp escalation in tensions between Russia and the United States after Washington launched 59 cruise missiles against an air base in Syria in retaliation for a deadly toxic gas attack that killed scores of people.

She said the Russian naval manoeuvres had been matched by increased persistent cyber attacks by Moscow, and a steady number of unprofessional "fly bys" by Russian aircraft of US and other allied vessels at sea.

In pictures: Russian air strikes in Syria Show all 19 1 /19 In pictures: Russian air strikes in Syria In pictures: Russian air strikes in Syria Syrian boys cry following Russian air strikes on the rebel-held Fardous neighbourhood of the northern embattled Syrian city of Aleppo Getty In pictures: Russian air strikes in Syria Russian defense ministry spokesman Major General Igor Konashenkov speaks to the media in Moscow, Russia. Konashenkov strongly warned the United States against striking Syrian government forces and issued a thinly-veiled threat to use Russian air defense assets to protect them AP In pictures: Russian air strikes in Syria Syrians wait to receive treatment at a hospital following Russian air strikes on the rebel-held Fardous neighbourhood of the northern embattled Syrian city of Alepp Getty In pictures: Russian air strikes in Syria Russian Deputy Defense Minister Anatoly Antonov speaks at a briefing in the Defense Ministry in Moscow, Russia. Antonov said the Russian air strikes in Syria have killed about 35,000 militants, including about 2,700 residents of Russia AP In pictures: Russian air strikes in Syria Jameel Mustafa Habboush, receives oxygen from civil defence volunteers, known as the white helmets, as they rescue him from under the rubble of a building following Russian air strikes on the rebel-held Fardous neighbourhood of the northern embattled Syrian city of Aleppo Getty In pictures: Russian air strikes in Syria Civil defence members rest amidst rubble in a site hit by what activists said were airstrikes carried out by the Russian air force in the town of Douma, eastern Ghouta in Damascus, Syria Reuters In pictures: Russian air strikes in Syria A girl carrying a baby inspects damage in a site hit by what activists said were airstrikes carried out by the Russian air force in the town of Douma, eastern Ghouta in Damascus, Syria Reuters In pictures: Russian air strikes in Syria Civilians and civil defence members look for survivors at a site damaged after Russian air strikes on the Syrian rebel-held city of Idlib, Syria Reuters In pictures: Russian air strikes in Syria Civilians and civil defence members carry an injured woman on a stretcher at a site damaged after Russian air strikes on the Syrian rebel-held city of Idlib, Syria Reuters In pictures: Russian air strikes in Syria Volunteers from Syria Civil Defence, also known as the White Helmets, help civilians after Russia carried out its first airstrikes in Syria In pictures: Russian air strikes in Syria The aftermath of Russian airstrike in Talbiseh, Syria In pictures: Russian air strikes in Syria Smoke billows from buildings in Talbiseh, in Homs province, western Syria, after airstrikes by Russian warplanes AP In pictures: Russian air strikes in Syria Russian Air Forces carry out an air strike in the ISIS controlled Al-Raqqah Governorate. Russia's KAB-500s bombs completely destroy the Liwa al-Haqq command unit In pictures: Russian air strikes in Syria Caspian Flotilla of the Russian Navy firing Kalibr cruise missiles against remote Isis targets in Syria Â© TASS/ITAR-TASS Photo/Corbis In pictures: Russian air strikes in Syria Russia claimed it hit eight Isis targets, including a "terrorist HQ and co-ordination centre" that was completely destroyed In pictures: Russian air strikes in Syria A video grab taken from the footage made available on the Russian Defence Ministry's official website, purporting to show an airstrike in Syria In pictures: Russian air strikes in Syria A release from the Russian defence ministry purportedly showing targets in Syria being hit In pictures: Russian air strikes in Syria Russia launched air strikes in war-torn Syria, its first military engagement outside the former Soviet Union since the occupation of Afghanistan in 1979. Russian warplanes carried out strikes in three Syrian provinces along with regime aircraft as Putin seeks to steal US President Barack Obama's thunder by pushing a rival plan to defeat Isis militants in Syria In pictures: Russian air strikes in Syria Caspian Flotilla of the Russian Navy firing Kalibr cruise missiles against remote Isis targets in Syria, a thousand kilometres away. The targets include ammunition factories, ammunition and fuel depots, command centres, and training camps Â© TASS/ITAR-TASS Photo/Corbis

Ties between Moscow and the West have been strained since Russia's annexation of the Crimea region of Ukraine in 2014 and its support for separatists in eastern Ukraine.

Nato has built up physical forces in Poland and the Baltic states to build up a deterrent and underscore the strength of the alliance, but US and European officials are also increasingly concerned about what they describe as Moscow's use of propaganda and cyber attacks to influence Western elections.

Russia denies Washington's claim Moscow sought to influence the US election, and views Nato's buildup of troops in Europe as a provocation.

Ms Howard said members of Nato had rallied to increase their capabilities and send a clear signal about the strength and resolve of the alliance.

She hailed a recent agreement by Germany and Norway to build new submarines together as a sign of increased cooperation and said she would welcome further efforts by European partners to pool resources.