One person has been killed and more than 50 injured in two separate explosions on buses in Sri Lanka.

Both explosions occurred in Monaragala district in the east of the island.

No group has said it carried out the attacks, which follow three other bus-bomb incidents over the last week. But police say they blame the Tamil Tiger rebel group.

Reports say the first bomb went off at a bus station in Bibile, some 160 km (100 miles) east of the capital Colombo.

The explosion is said to have damaged the rear of the bus.

The other exploded on a bus travelling between Medagama and Monoragala, south of Bibile.

One report quoted police saying the casualties could have been higher but for a mechanical failure in the second bus.

"The driver had asked passengers to get off because of a problem with the gearbox," a police spokesman said.

"There were about 250 grams of explosives in each bomb," he said.

Year of war

The BBC's Susannah Price in Colombo says the explosions suggest that the Tamil Tigers may again be focusing on civilian targets.

The Bishop of Jaffna has said the Tigers have designated this the year of war.

Last week, some 33 people were hurt when bombs exploded in three buses a day before the country marked its 52nd anniversary of independence from colonial rule.

The Tamil Tigers are fighting for a separate homeland for minority Tamils in the north and east of the island.

Last week, Sri Lankan President Chandrika Kumaratunga made an offer of peace to the rebels.

She has proposed a devolution package which will offer limited autonomy to Tamil majority areas in the north and the east.

There has been no reaction from the Tamil Tigers to the proposal.