Associated Press
In this Tuesday April 30, 2013 file citizen journalism image provided by The Syrian Revolution Against Bashar Assad which has been authenticated based on its contents and other AP reporting, shows Syrian rebels, right, standing near a damaged warplane, at Abu Dhour military airbase after it fell due to clashes with rebels, in the northern province of Idlib, Syria. A Syrian military official said Wednesday that an investigation is underway into the alleged downing of a U.S. reconnaissance aircraft by Syrian air defenses along the country's Mediterranean coast.

BEIRUT — A Syrian military official said Wednesday that an investigation is underway into the alleged downing of a U.S. reconnaissance aircraft by Syrian air defenses along the country's Mediterranean coast.

A U.S. official said Tuesday that a U.S. Predator drone went down in Syria, but that it was unclear whether it was shot down. The official, who spoke on condition of anonymity because the Pentagon had not yet announced the loss, said U.S. officials were trying to determine why operators lost control of the drone.

The Syrian official said the aircraft entered Syrian airspace from the sea and was shot down over Ras Shamra, seven kilometers (four miles) north of the coastal city of Latakia. He said the aircraft was flying over an area devoid of "armed gangs," using a term often used by Syrian authorities to refer to opposition groups fighting President Bashar Assad's forces.

The official spoke on condition of anonymity because he was not authorized to give statements to the press.

State television on Tuesday night broadcast footage of what it said was the wreckage, including a wheel and electronic parts. Soldiers in camouflage could be seen loading some of the debris into the back of a truck.

If confirmed, it would be the first American aircraft to go down over Syria since the U.S. expanded its aerial campaign against the Islamic State extremist group to the country in September.

More than 220,000 people have been killed in four years of conflict in Syria, which started with largely peaceful protests calling for reforms and escalated into civil war following a brutal government crackdown.

In a statement released late Tuesday, the main Western-backed Syrian opposition group called on the United Nations to send a fact-finding mission to investigate an alleged poison gas attack on a rebel-held northern town.

The Syrian National Coalition and activists inside Syria say the government carried out a chlorine gas attack on the town of Sarmin late Monday, killing six people and leaving dozens more struggling to breathe. Syrian authorities denied the allegations.

In the statement, Coalition vice president Hisham Marwa called for an on-site UN investigation as soon as possible. He also demanded the Security Council enforce a recent resolution that condemns the use of toxic chemicals such as chlorine in Syria and threatens military action in case of violations.

"The UN Security Council must take all necessary measures that ensure the enforcement of the resolution," Marwa said.

The international medical humanitarian organization, Medecins Sans Frontieres (MSF), said six people were killed and 70 others poisoned in the attack, quoting reports by Syrian doctors in contact with the group.

It said the events and symptoms described by the medical staff of the hospital clearly indicate the presence of chlorine poisoning.

"Attacking a village and its civilian population with chlorine shows once again that the Syrian conflict knows no limits," said Dr. Mego Terzian, MSF president.

The spokesman for the Organization for the Prohibition of Chemical Weapons, Peter Sawczak, said Wednesday the watchdog agency views "any allegations of chemical weapons use with concern and we are monitoring the situation closely."

Monday's purported attack would be one of the most serious uses of poison gas in Syria since a deadly chemical attack outside Damascus in August 2013.

An OPCW fact-finding mission concluded "with a high degree of confidence" that chlorine was used on three rebel-held villages in Syria last year, killing 13 people. It did not assign blame. Last month, the OPCW condemned the use of chlorine in Syria as a breach of international law.

Despite the new Security Council resolution, an international consensus on who was responsible for a violation would be needed to take any action, which would likely prove difficult. The Security Council remains divided over Syria's civil war, with the U.S. and its allies supporting the opposition and Russia backing Syrian President Bashar Assad.

Associated Press writers Ryan Lucas in Beirut and Robert Burns in Washington contributed to this report.