Panichachankani, Sri Lanka ? Mainstream Tamil Tiger guerrillas advanced on a heavily armed breakaway faction Friday in a vicious gun and mortar battle that killed at least nine people, wounded 20 and imperiled Sri Lanka’s fragile 2-year-old cease-fire.

It was the worst fighting since the 2002 truce halted the 19-year civil war, and came a week after voters rejected the government that had negotiated the cease-fire. The balloting elected a Parliament that backs the hard-line president.

Sri Lankan army troops were told to stay out of the rebel conflict, but the fighting was taking place within a miles of army camps, where armed soldiers listened by radios to news of the factional guerrilla fighting along the Vergual River, 140 miles east of the capital, Colombo.

After hours of mortar and machine-gun fire, about 500 fighters from the breakaway group — including women and teenage boys and girls — withdrew from the area, claiming they were repositioning not retreating.

“About 1,000 … people came and attacked us, so this is a tactical withdrawal and we are going to set up our new defense line,” S. Kumar, a senior commander of the breakaway group, said.

He said more fighters from the mainstream Liberation Tigers of Tamileelam were moving to fortify their freshly gained positions on the opposing side, indicating another offensive maneuver was likely.

Members of the main 9,000-strong Tamil Tiger rebel group based in the north seized territory from the breakaway 6,000-strong eastern faction, led by a charismatic commander Vinayagamoorthy Muralitharan, known as Karuna.

The two sides had been squared off since Karuna announced the schism March 3 in a dispute of regionalism rivalry and political strategy.

For two decades the Tamil Tigers fought government troops in a bloody separatist conflict that claimed an estimated 65,000 lives.

More than 3,500 terrified villagers had fled their homes by Friday evening and more were planning to come, they said.

Members of a breakaway faction of the Tamil Tiger rebels retreat from their positions at the Vergual River in the rebel-controlled Tamil Tiger area in eastern Sri Lanka. Rival Tamil Tiger guerrilla factions fought with mortars and guns Friday in a battle that killed at least nine people, wounded 20 and endangered Sri Lanka's fragile peace accord.