A powerful bomb has ripped through the main post office in the northern Sri Lankan town of Vavuniya.

At least 11 people were killed and about 70 injured in the blast.

The attack comes as a Norwegian delegation is in Sri Lanka to try to broker peace talks between the government and Tamil Tiger rebels.

The Tigers are fighting for an independent homeland in northern Sri Lanka and have been blamed for a number of recent attacks, including an assassination attempt on President Chandrika Kumaratunga

Officials said the parcel bomb went off inside Vavuniya post office - which is opposite a police station - totally destroying it.

The defence ministry said that 12 soldiers and seven police officers were among the injured.

A number of security personnel, who had just been paid, were in the post office to send money orders home to their families.

However, most of the casualties were civilians.

The BBC's Susannah Price in Colombo says the bomb appears to have been timed to cause maximum casualties among the security forces.

Defence Ministry spokesman Brigadier Palitha Fernando said: "The bomb was placed in the letter box meant for the outgoing foreign mail.

"The attackers knew that the soldiers would come today to send the money."

He pinned blame for the blast on the Tamil Tigers.

Tight security

Vavuniya is a government-controlled frontier town lying 220km (135 miles) northeast of the capital, Colombo, and is home to a large military base.

It is only 20km from the area controlled by the Tamil Tiger guerrillas.

The bombing came despite tight security throughout the country.

The Tigers have stepped up their activities recently in and around Colombo, killing more than 50 people in suicide bomb explosions.

Late last year, they captured a huge swathe of territory just north of Vavuniya and there were fears the town itself could come under attack.

More than 55,000 people have been killed since fighting began in 1983.