BEIRUT (Reuters, AFP) - At least 32 Islamic State in Iraq and Syria (ISIS) members, including four of its leaders, were killed in air strikes and a US special forces raid that targeted the group in eastern Syria, a group monitoring the Syrian war said on Sunday.

US officials said the raid killed a senior ISIS leader identified as a Tunisian who helped to manage its black-market sales of oil and gas to raise funds. A US official said that about a dozen fighters were killed in the raid.

British-based monitoring group the Syrian Observatory for Human Rights gathers its information from sources in the region.

"The US operation killed 32 members of ISIS, among them four officials, including ISIS oil chief Abu Sayyaf, the deputy ISIS defence minister, and an ISIS communications official," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.

The operation in the eastern Deir al-Zor province marked a departure from Washington's strategy of relying primarily on air strikes to target militants in the area. US officials have said "about a dozen" people were killed in the operation on Friday night, which was conducted by Iraq-based US commandos in order to capture Abu Sayyaf.

Abdel Rahman said three of the four leading officials killed in the raid were from North Africa, but that the ISIS communications official was Syrian.

US President Barack Obama approved the special forces operation, a rare use of "boots on the ground" by the United States, which has fought the extremists almost entirely from the air.

The operation targeted an ISIS compound at al-Omar, one of Syria's largest oil fields, which is located in the eastern Deir Ezzor province.

A US official speaking on condition of anonymity said the commandos engaged the jihadists "at very close quarters... there was hand-to-hand combat".

US Secretary of Defence Ash Carter called the operation a "significant blow" to ISIS, while Adam Schiff, a Democrat on the House intelligence committee, said US attacks "have put increasing pressure on the economics undergirding the terrorist organisation".