Russia has dispatched a military reconnaissance ship into the eastern Mediterranean, where five US warships are operating in the lead-up to a widely expected air strike in Syria.

The reconnaissance ship Priazovye departed for the Syrian coast on Sunday to keep tabs on the situation there, the state news agency Itar-Tass quoted a military source as saying.

"This is the normal policy of any fleet in the case of an increase in tensions in any ocean or sea," the source said.

The deployment of the Russian ship follows the arrival of an additional US destroyer in the eastern Mediterranean late last week. The USS Stout, a guided missile destroyer, was sent to relieve the USS Mahan, but a defence official told AFP that both ships might remain in the area for now. Along with the Ramage, the Barry and the Gravely, the destroyers could launch Tomahawk missiles at targets in Syria if the US president, Barack Obama, orders an attack.

Meanwhile, a group of American ships led by the aircraft carrier Nimitz are deployed in the area of the Arabian Sea.

The US has been preparing for possible air strikes against the regime of Bashar al-Assad in retaliation for an alleged gas attack that killed more than 1,400 people outside Damascus. While the US has blamed the Syrian government, Russia has argued that rebel forces probably staged it to provoke foreign intervention against Assad.

At a press conference last Monday, the foreign minister, Sergei Lavrov, again denounced any foreign intervention but said Russia was "not planning to go to war with anyone" over Syria.

On Monday, Lavrov said a US strike would put the proposed Geneva II peace conference in serious doubt, Itar-Tass reported.

"If the action announced by the president of the United States unfortunately occurs, it will put off prospects for the forum for a long time, if not forever," Lavrov said.

Also on Monday, Lavrov said Russia remained unconvinced of US allegations that the Assad regime was behind the chemical attack after a meeting between the American ambassador to Russia, Michael McFaul, and a senior Russian diplomat. The material presented by the United States contained no facts and "absolutely does not convince us", Lavrov said.