Russia has positioned about a half dozen tanks at an airfield at the centre of a military buildup in Syria, two US officials said yesterday, adding that the intentions of Moscow’s latest deployment of heavy military equipment were unclear.

Moscow has come under increased international pressure in recent days to explain its moves in Syria, where the Kremlin has been supporting Syrian President Bashar al-Assad in a four-and-a-half-year war. The Pentagon declined to directly comment on the Reuters report, saying it could not discuss US intelligence. But a spokesman said recent actions by Moscow suggested plans to establish a forward air operating base.

“We have seen movement of people and things that would indicate that they plan to use that base there, south of Latakia, as a forward air operating base,” Pentagon spokesman Captain Jeff Davis said.One of the US officials, who spoke on condition of anonymity to discuss intelligence matters, said seven Russian T-90 tanks had been observed at the airfield near Latakia, an Assad stronghold. The two US officials said Russia had also stationed artillery that appeared to be arrayed defensively to protect Russian personnel stationed there.

Reuters has previously reported that Russia deployed about 200 naval infantry soldiers to the airfield, as well as temporary housing units, a portable air traffic control station and components for an air defence system. Moscow has been sending about two military cargo flights a day to the airfield over the past week, US officials say. A diplomatic source said the Russians were working to improve the airfield.

“There have been trucks going in and out. It appears the runway is not suited to some types of aircraft yet and they have been doing some improvements,” the diplomat said.

Russia has said it will continue providing military supplies to Syria and that its assistance to the Syrian army is in line with international law. The US is using Syrian airspace to lead a campaign of air strikes against Islamic State. A greater Russian presence raises the prospect of the Cold War superpower foes encountering each other on the battlefield.

So far, Russia has not sent combat aircraft or helicopter gunships to the airfield, the Pentagon said.

Both Moscow and Washington say their enemy is Islamic State, whose Islamist fighters control large parts of Syria and Iraq. But Russia supports the government of Assad in Syria, while the US says his presence makes the situation worse.