MANILA, Aug 12 (Reuters) - Top Philippine military officials visited a remote southern island on Sunday where nearly 60 people were killed last week in clashes with Muslim rebels as signs mounted that the government was planning a big offensive.

Twenty-six soldiers were killed in the fighting on Jolo island on Thursday, military officials have said. They said 32 rebels had died, and also a young boy who was caught in crossfire.

Military chief General Hermogenes Esperon and chief of army staff Lieutenant-General Romeo Tolentino visited Jolo to inspect troops as reinforcements were flown in from the mainland.

"The rule of law must prevail," Tolentino later told reporters. "For me, (I can do it in) 10 days."

On Saturday, President Gloria Macapagal Arroyo said no mercy would be shown to the rebels.

"We cannot allow terrorists to hold the south hostage to their agenda of mayhem and bloodsport," she said.

"We seek peace with those with peaceful intentions. But we also seek justice for our soldiers, civilians and communities affected by this conflict."

She also ordered Tolentino to shift his headquarters to the southern city of Zamboanga, which is close to Jolo, until the situation was resolved.

There were no signs of fighting on Sunday on Jolo, a moutainous island carpeted with forest.

But more than 10,000 people have fled from their homes and farms around three towns where the fighting erupted on Thursday.

Officials have said two battalions, or about 1,000 troops, will join the 5,000 soldiers already on Jolo.

About 100 U.S. special forces are also on Jolo to help train the Philippine military. They are forbidden from fighting under Philippine law.

The rebels are believed to be from Abu Sayyaf, a group linked to al Qaeda, and from Moro National Liberation Front (MNLF), a Muslim rebel group that signed a peace deal with the largely Roman Catholic central government in 1996.

The MNLF has said its members attacked troops after one of its leaders was killed, and that it had asked the Organisation of the Islamic Conference (OIC) to help stop the fighting.

Due to family ties on Jolo, there are close links between the Abu Sayyaf and the MNLF and sometimes an overlap in allegiance.

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