The United States lost one of its Predator drone aircraft over northwest Syria on Tuesday, U.S. officials said, as Syrian state media reported its air defenses brought down the spy plane in the government-controlled Latakia province.

If Syrian President Bashar al-Assad's forces took down the U.S. aircraft - something U.S. officials said was not immediately certain - it would raise the stakes in the U.S.-led bombing campaign against Islamic State militants that began in Syria in late September.

The United States has previously described Assad's air defenses as "passive," meaning they have not engaged the U.S.-led coalition's aircraft as American and other planes carry out strikes against militants.

The U.S. airstrikes have not targeted Assad's forces or military infrastructure.

Tuesday's incident took place sometime around 7:40 pm in Syria, when the United Stateslost contact with an unarmed MQ-1 Predator aircraft operating over northwest Syria, a U.S. official said.

A second U.S. official, speaking on condition of anonymity, said the aircraft took off from a base in Turkey and a third official confirmed it was operating over Latakia province.

A fourth U.S. official said the aircraft was destroyed but U.S. officials were not ready to say what happened - much less whether Assad's forces might have engaged the aircraft. They said the cause of the incident was unclear.

"At this time, we have no information to corroborate press reports that the aircraft was shot down," said the first U.S. official, who asked to be described only as a defense official.

"We are looking into the incident and will provide more details when available."

It was the first such incident since the U.S.-led coalition began carrying out air strikes against the hardline militant Islamic State group, first in Iraq in August and then in Syrialate the next month.

But it was not the first loss of a coalition aircraft in Syria.

In December, a Jordanian pilot was captured by Islamic State militants after his warplane came down in northeast Syria. The militants released a video in February showing the pilot being burned alive in a cage.

Earlier, Syria's state news agency SANA said its air defenses brought down an American spy plane, without specifying what model of aircraft.

"Syrian air defenses brought down a hostile U.S. surveillance plane in northern Latakia,"SANA said in a bulletin, without elaborating.