COLOMBO, Sri Lanka - The Sri Lankan military says a suspected Tamil Tiger rebel hurled a hand grenade at a bus full of war-displaced refugees, killing a woman and wounding 13 others.

The bus was attacked in Puliyankulam village in the north while transporting people who had fled the embattled region for government territory.

Rebel officials couldn't be contacted for comment.

The military's claim could not be independently verified because independent journalists are barred from the war zone.

A 59-year-old woman was killed and the wounded included four children.

The government has accused the Tigers -- who have recently lost their main strongholds to government forces and are cornered in a small sliver of coastal land -- of holding scores of people as human shields.

It also accuses them of and killing civilians who want to escape. The rebels have denied the allegations.

The Red Cross said it is negotiating with the government and rebels to allow the sick and wounded in the war zone to travel to hospitals in government territory.

International Committee of the Red Cross spokeswoman Sarasi Wijeratne said wounded civilians continue to flock to a makeshift hospital in rebel-held Putumattalan village.

It is overwhelmed despite moving 640 patients and their relatives from the facility earlier this week.

Thurairajah Varatharajah, a doctor at the hospital, said 300 more wounded patients arrived since the evacuations, and about 100 more patients were suffering from various illnesses.

The Sri Lankan military says it is close to crushing the rebels and ending their 25-year campaign for an independent homeland for ethnic minority Tamils.

Tamils, who make up 18 per cent of the country's population, have been marginalized by successive governments controlled by ethnic Sinhalese.

More than 70,000 have been killed in 25 years of violence.