(Updates with six more Tigers reported shot dead)

By Simon Gardner and Ranga Sirilal

COLOMBO, March 23 (Reuters) - At least 26 Tamil Tiger rebels and three soldiers were killed in clashes in northwestern and eastern Sri Lanka on Friday, the military said, as analysts warned that renewed civil war is spreading.

The army confirmed troops were trying to neutralise heavy rebel guns in northwestern Mannar district, but refused to say whether they had entered terrain the rebels control under the terms of a now-battered 2002 truce as the Tigers claim.

"The LTTE is attacking with mortars ... without considering the safety of the civilians in the area. Three soldiers were killed and 4 injured," military spokesman Brigadier Prasad Samarasinghe said.

"We have retaliated to neutralise them and we have observed more than 20 Tiger dead bodies."

In a separate incident, troops shot dead six Tigers who ambushed a route-clearing patrol in the eastern district of Batticaloa, taking the death toll in the past 48 hours to at least 42.

The Tigers said they were fighting fierce artillery battles with hundreds of troops who had crossed into Mannar. They were not immediately available for comment on the death toll.

The clash, some 1.2 miles (2 km) inside rebel lines, came as sporadic fighting continued in the east -- where troops have evicted the Tigers from around 600 square km (230 square miles) of land amid a declared drive to destroy them militarily.

"This morning a contingent of army troops intruded into our parts of Mannar district ... and are holding 120 families in a village as human shields while they are firing at us," Tiger military spokesman Rasiah Ilanthiraiyan said earlier from the rebels' northern stronghold of Kilinochchi.

Samarasinghe said troops had killed 13 rebels on Thursday in the northern districts of Vavuniya and Jaffna.

He said some of those slain wore characteristic Tiger-striped uniforms, and that troops had also recovered a stash of rebel equipment including a suicide bomber jacket and cyanide capsules in a lorry in the army-held Jaffna peninsula.

The Tigers denied that any of their fighters had been killed on Thursday, saying the dead must be civilians.

WAR SPREADING

Friday's fighting is the latest in a string of land and sea clashes that have killed some 4,000 troops, civilians and rebels in the past 15 months and which analysts expect to spread.

"There are strong indications that heavy fighting will shift to the northern theatre from the east," said Iqbal Athas of Jane's Defence Weekly. "This is a clear sign that the war is escalating."

Tiger rebels attacked five army camps in Batticaloa on Wednesday and tried to infiltrate government lines in the north, sparking fierce clashes that the military said killed at least 17 people and wounded dozens.

The fighting has driven an estimated 155,000-165,000 people from their homes in the east, many now living in cramped, dusty refugee camps. Agencies call it a major humanitarian emergency.

The rebels, who seek an independent state, have warned of a bloodbath if the military tries to capture more territory.

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