COLOMBO, Sri Lanka — A rebel suicide bomber attacked a procession of Muslims celebrating a religious holiday today in southern Sri Lanka, killing 14 people and critically wounding a government minister.

Officials blamed the Tamil Tigers for the blast, saying the rebels had grown desperate in the face of a relentless government offensive that has brought them to the brink of defeat after more than a quarter century of civil war.

Meanwhile, heavy artillery attacks in the war zone today killed at least 49 ethnic Tamil civilians and wounded hundreds of others, the top government health official in the war zone said.

Human rights groups and aid workers have expressed growing concern for the fate of the tens of thousands of civilians trapped in the conflict zone amid the escalating violence.

As fighting raged in the north, the suicide bomber struck in the southern town of Akuressa, apparently targeting six ministers as they led a procession toward a mosque to celebrate Mawlid, which commemorates the prophet Mohammed’s birthday.

Television footage showed men in white robes and caps slowly parading down the street before the blast sent them running in all directions. Charred, twisted bodies filled the street, their clothes nearly incinerated by the explosion just outside the mosque compound’s gates.

“I heard a huge sound, and then I saw people had fallen everywhere. They were covered with blood and flesh, and the wounded people were screaming,” Ahamed Nafri, 29, said by telephone from the hospital in the nearby town of Matara.

Police and bystanders were seen lifting the badly bleeding Mahinda Wijesekara, minister of posts and telecommunications, into a van.

Aruna Jayasekera, a doctor at Matara hospital, said Wijesekera was in critical condition and had been airlifted to the capital for surgery to remove “blood and foreign objects” from his brain.

President Mahinda Rajapaksa’s office said the attack killed 14 people. Another 41 people wounded in the blast were being treated in Matara, Jayasekera said.

The attack came as government forces stood poised to rout the Liberation Tigers of Tamil Eelam from their last stronghold in northeastern Sri Lanka after a 20-month offensive.

But today’s suicide attack near the southern tip of the island — if the work of the Tamil Tigers — shows the guerrillas still can launch strikes far from their traditional strongholds in the north and east, even in the face of battlefield defeat.

With most communication to the northern war zone severed, rebel spokesman were not immediately available for comment.

The rebels have fought since 1983 for an independent state for the Tamil minority, which suffered decades of marginalization at the hands of governments dominated by the Sinhalese majority. More than 70,000 people have been killed.

Dr. Thurairaja Varatharajah, the top government health official in the war zone, said shelling continued to hit a government designated civilian refuge inside rebel territory today as heavy rains flooded trenches and forced families out into the open.

By the afternoon, 279 wounded civilians were brought to the makeshift hospital he runs in the area, and 43 of them died because of lack of adequate care, he said. Many of the wounded were being treated under trees in the rain. Another six bodies were brought to the hospital’s morgue, he said.

Since the beginning of March, 1,205 wounded civilians were brought to the hospital and 218 people either died at the facility or were brought to the morgue by family members, he said. However, many families have stopped bringing their dead to the hospital because of the heavy shelling, health officials say.

The army denies shelling the area.

Neil Buhne, the United Nations’ top official in Sri Lanka, reiterated the international organization’s call for a pause in the fighting to let civilians flee the area.