Ancient statues and other artefacts have been stolen from Syria's National Museum in Damascus, officials say.

The theft was discovered on Monday, when staff reportedly found that one of the museum's doors had been broken from the inside.

The six missing statues were made of marble and dated back to the Roman era, one official told the Associated Press.

Syria's Directorate-General for Antiquities and Museums said it had opened an investigation to determine the "circumstances surrounding the loss of a number of exhibits", and that measures had been taken to strengthen protection and monitoring systems.

The head of internal security in Damascus province, Brig-Gen Osama Atkeh, was cited by the state-run Sana news agency as saying that security forces were investigating the theft, which he said had targeted several "archaeological statues and rare collectibles".