(Updates death toll, adds Tiger comment) By Ranga Sirilal COLOMBO, July 24 (Reuters) - Sri Lanka's Tamil Tigers ambushed an army bus killing 10 soldiers in the island's restive north on Tuesday hours after killing four village policemen, the military said. The attacks were the latest in a spree of ambushes blamed on the rebels amid a new chapter in a two decade civil war. "A Claymore (mine) exploded targeting a bus carrying troops from Mannar to Vavuniya," a spokesman at the Media Centre for National Security said, declining to be named in line with policy. "It was definitely the Tigers." He said the death toll from the blast had risen from 9 to 10, but gave no further details. Six soldiers and 8 civilians, were wounded in the attack. Two of the civilians were in critical condition. The town of Vavuniya is the last major staging post before the southern front line that separates government from rebel-held territory in the north while Mannar is in the northwest. Hours earlier suspected rebels killed four 'homeguards', or rural police, in the same district. Those killings in turn came on the heels of a rash of land and sea clashes, ambushes and air raids that have killed an estimated 4,500 people since last year. Homeguards are a force of police recruited and armed to guard their own villages and wear a distinct light purple uniform. The Tigers said they had no immediate details about the attacks, but routinely deny involvement in roadside bomb blasts on security forces -- denials analysts dismiss. However the Tigers have deployed fighters along the the front line in Vavuniya and neighbouring Mannar, and said pre-emptive strikes on military targets such as camps remained an option. "We have stationed our troops waiting in all the possible parts and any infiltrators or any invaders will be pushed back," Tiger military spokesman said by telephone from the Tigers' northern stronghold of Kilinochchi. "I do not rule out pre-emptive strikes." Evicted from swathes of the east by military offensives in recent months, the Tigers have vowed to switch to guerrilla tactic mode to strike major economic and military targets in a bid to cripple the island's $23 billion economy. They say peace is impossible with President Mahinda Rajapaksa, who has vowed to wrest control of all rebel-held territory. Analysts say that sets the stage for a bloody fight for the north, where fighting is now focused. Nearly 70,000 people have been killed since 1983, and analysts see no clear winner on the horizon.
