At least five police officers have died in an armed clash with gunmen in eastern Sabah state, officials in Malaysia say.
Police are investigating whether the firefight in Semporna on Saturday night was linked to an armed incursion by Filipino men 150km (90 miles) away.
At least 100 Filipinos landed by boat in the Lahad Datu district last month.
They say documents dating back to the 19th Century are proof that the area belongs to them.
The Muslim clan, which calls itself the Royal Army of Sulu, has occupied the village of Lahad Datu since early February.
On Friday, 12 Filipinos and two Malaysian police officers were killed in a gun battle there.
In the latest incident, national police chief Ismail Omar said that five policemen were killed in an "ambush by unidentified gunmen". One report said two attackers also died.
The Lahad Datu crisis began when a group of at least 100 clan members were led into the region in early February by Agbimuddin Kiram, the younger brother of the self-proclaimed Sultan of Sulu Jamalul Kiram III.
The Sulu Sultanate once spread over several southern Philippine islands as well as parts of Borneo, and claimed Sabah as its own before it was designated a British protectorate in the 1800s.
Sabah became part of Malaysia in 1963, and the country still pays a token rent to the Sulu Sultanate each year.
The Royal Army of Sulu wants Malaysia to recognise it as the rightful owner of Sabah, and to renegotiate the terms of the old lease - something Malaysia has made clear it has no intention of doing.