The US was joined by Saudi Arabia and the UAE in striking modular oil refineries in eastern Syria, in an effort to choke off Islamic State finances, officials said.

One US official told Reuters that such refineries could produce about $2 million a day in oil revenue.

Modular refineries are pre-fabricated and constructed off-site so they can be transported and made operational quickly.

The strikes hit facilities around al Mayadin, al Hasakah, and Abu Kamal, the US military said.

At least 14 Islamic State fighters were killed in air strikes by US-led forces overnight in northeast Syria, a group monitoring the war said.

The strikes also killed at least five civilians, said Rami Abdulrahman, who runs the Britain-based Syrian Observatory for Human Rights.

The initial days of US strikes suggest another aim is to hamper Islamic State's ability to operate across the Syria-Iraq frontier.  - Reuters