At least six people have been killed and the head of the Sri Lankan army has been critically injured after a female suicide bomber attacked the army's headquarters in Colombo.

At least five bodyguards and the bomber were killed in the attack, which took place as the car carrying the army chief Lieutenant General Sareth Fonseka, arrived at the base.

Dozens of ambulances were rushed to the military compound to evacuate the wounded.

Fonseka, a high-profile military commander with 35 years experience in the infantry, was appointed to the top post after President Mahinda Rajapakse took office in November.

He has taken a hard line against the Tamil Tiger rebel group, advocating a tougher stance against the rebels in the ongoing peace process.

The Tigers, who are observing a shaky ceasefire with the government since 2002, have been blamed for suicide attacks in the past.

The blast came during a visit to Sri Lanka by Norwegian peace envoy Jon Hanssen-Bauer who hopes to restart peace negotiations between the two sides.

Earlier on Tuesday, the Tigers had called on Hanssen-Bauer to pressure the government to accept its terms for peace talks.

The government accuses the Tigers of being behind an upsurge in bomb attacks in the north-east of the island that has left at least 70 people dead in the past weeks.

The Tigers blame government militias for causing ethnic tensions on the island between the Sinhalese majority and Tamils.

On Tuesday, US-based Human Rights Watch accused the government of ignoring attacks on ethnic Tamils.

PHOTO CAPTION

A soldier stands guard at the entrance of the army headquarters after a suicide bomb attack in Colombo, Sri Lanka, Tuesday, April 25, 2006. (AP)