A brief fire-fight broke out late Sunday night in a southern Philippine province under the martial law as security forces continued to pursue rebellious para-military soldiers loyal to a local political clan, the top police official said Monday.

National Police Director General Jesus Versoza told reporters that however there is no casualty on the government side during the 10-minute clash at the Datu Unsay town in volatile Maguindanao province.

He said policemen patrolling the town at night were fired upon by roughly 20 to 30 armed men believed to be loyal to the Ampatuan clan. Police called back-ups and fired back before the armed rebels escaped, Versoza said.

It is the first major clash in Maguindanao since President Gloira Macapagal-Arroyo imposed the martial law in the province late last Friday, following the gruesome massacre of 57 civilians on Nov. 23, the worst case of election-related violence in the country.

Andal Ampatuan Jr., mayor of the Datu Unsay, was arrested and charged as the prime suspect behind the massacre. A couple of other members of the Ampatuan clan have also been put in custody.

His family has been in control of the province since 2001. Sixteen out of 22 towns in Maguindanao were headed by members of the Ampatuan clan, Interior Secretary Ronaldo Puno said.

Versoza and Puno said around 2,400 para-military soldiers have massed up in parts of Maguindanao since Andal Jr.'s arrest on Nov. 26 and they attempted to stage rebellion.

Puno said the government will lift the martial law once rebellion tries were all crushed and officials are conducting conversations to convince thousands of para-military soldiers running at large to return to the folds of law.

"We try to avert violence and prevent bloodsheds. The ideal way is they follow the Constitution again and we are entitled to remove the martial law," he said.