(Adds more soldiers killed in fresh fighting)

MANILA, Aug 9 (Reuters) - Muslim rebels killed at least 20 Philippine soldiers on Thursday in gun battles on the remote southern island of Jolo, the army said.

At least nine soldiers were killed and two were wounded in an ambush in the morning near the town of Maimbung, where the troops were headed to buy food, Major-General Ruben Rafael said. One of the wounded later died.

Reinforcements were rushed to the area and troops began pursuing the rebels, officials said.

In a gun battle later in the day, at least 10 soldiers were killed in mountains near Maimbung, said Major Eugene Batara, a military spokesman in the city of Zamboanga, the headquarters of the Philippines' southern military command.

There was no immediate word of any rebel casualties.

The tropical isle of Jolo, a base for Muslim militants in the largely Catholic country, has seen an escalation in violence after the army started collecting unlicensed guns from civilians.

An army spokesman, Lieutenant-Colonel Ernesto Torres, said about 100 rebels from the Abu Sayyaf and a rogue faction of the Moro National Liberation Front (MNLF) were believed to be behind the ambush in the morning, retaliating for losses in an earlier clash.

On Wednesday, soldiers killed four Muslim rebels in a brief gun battle in nearby Parang town, where a soldier was also killed and five were wounded.

But, the mainstream MNLF, which signed a peace deal with the government in 1996, claimed it was behind the ambush, saying it was retaliation for the deaths of five people during an army offensive a day earlier.

"It was not the Abu Sayyaf," Hatimil Hassan, the deputy chairman of the MNLF, said on local TV. "It was our troops. It was the military's fault. They started it all."

Last month, members of the Moro Islamic Liberation Front (MILF), the country's largest Muslim separatist group, killed 14 Marines in an attack on the nearby island of Basilan. Ten of the soldiers were beheaded but the MILF, which is meant to be talking peace with Manila, has denied its members mutilated the troops.

The military also blames members of the Abu Sayyaf for the decapitations. Due to family ties on Jolo and Basilan, there are close links between the Abu Sayyaf, the MNLF and the MILF and sometimes an overlap in membership.

The Philippine government wants to seal a peace deal with the MILF but has sworn to crush the Abu Sayyaf, which is blamed for the Philippines' worst terror attack -- a ferry bombing that killed more than 100 people in 2004.

The islands of the southern Philippines, especially Jolo and Basilan, are hotbeds of extremism. They are also home to bandit and pirate gangs that prey on shipping in the South China Sea.

About 13,000 Philippine troops are on the islands to contain about 2,000 rebels. About 100 U.S. special forces are also on Jolo to help train the Philippine military, but they are forbidden from fighting under Philippine law.

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