The Organization for Security and Cooperation in Europe's mission in eastern Ukraine says four of its armored cars were destroyed in an apparent arson attack.

It was unclear who carried out the attack in Donetsk, the main rebel-held city.

The white sport utility vehicles were parked outside the hotel that houses the OSCE observers.

The OSCE has had a mission in eastern Ukraine since March 2014 to monitor the conflict between the Russia-backed separatists and Ukrainian government troops, which has now killed at least 6,400 people.

The OSCE mission said in statements on Twitter that it had no plans to withdraw from Donetsk at this stage because of the apparent arson attack early Sunday.