WASHINGTON: Syrian rebels have recently obtained up to 40 shoulder-fired antiaircraft missiles, the Washington Post reported Thursday, citing Western and Middle Eastern intelligence officials.

Some of the missiles were supplied in the past weeks by Qatar, the newspaper reported, citing two unnamed Middle Eastern intelligence officials with knowledge of the matter.

"It should be worrying to everyone," one of the officials said. "When (Syrian President Bashar al-) Assad is finished, terrorists could end up with these, and commercial flights would be at risk."

The US government has opposed arming Syrian rebels with such weapons, fearing that they could eventually land in the hands of terrorists. US intelligence officials declined to comment on the report.

The report comes after the Syrian Observatory for Human Rights said Tuesday that the Syrian rebels downed an army helicopter with a ground-to-air missile.

"It is the first time that the rebels have shot down a helicopter with a surface-to-air missile," Observatory director Rami Abdel Rahman told AFP.

The Britain-based Observatory said the missile was part of a consignment newly received by the rebels that had the potential to change the balance of forces in the 20-month conflict.

More than 40,000 people have died since the conflict erupted in March 2011, according to the Observatory.