A suicide attack on the funeral of a key anti-Taliban cleric killed at least 20 people including one of Afghanistan's top policemen and wounded 52 in the southern city of Kandahar.

The blast ripped through a mosque in the centre of the city, the birthplace of the hardline Islamic Taliban regime that was ousted by US-led forces three and a half years ago, as hundreds of mourners gathered inside.

The attack was the worst in Afghanistan this year and one of the most serious since the fall of the Taliban, which gave shelter and support to Osama bin Laden's Al-Qaeda network.

Afghan interior ministry spokesman Lutfullah Mashal told AFP on Wednesday that the police chief of the capital Kabul, General Akram Khakraizwall, was among the dead. "It was a suicide attack by the enemies of Afghanistan and Islam. The investigation into the case has started," added Mashal.

The bombing came as prayers were given for Maulvi Abdullah Fayyaz, a close supporter of US-backed President Hamid Karzai. Fayyaz was gunned down on Sunday after recently speaking out against fugitive Taliban leader Mullah Omar. "Twenty people were killed and 42 were injured and hospitalised," the provincial governor, Gul Agha Shirzai, told reporters in Kandahar.

Interior Minister Ali Ahmed Jalali put the number of wounded at 52. "52 people were injured and 32 of them seriously enough to be hospitalised. Twenty others were discharged from the hospital after medication and went home," he told reporters in Kabul.

The bomber had been identified as an Arab, based on documents including an identity card found on the remains of his body, Governor Shirzai added. Arabs make up the bulk of the Al-Qaeda militants believed to remain in Afghanistan.

Witnesses said a man in a police uniform approached the police chief and bent over, pretending to reach for Khakraizwall's shoes, which he had taken off to enter the mosque in line with tradition.

"That was when he detonated his bomb. It was a terribly big explosion which killed Khakraizwall and his bodyguards and people around him," survivor Mohammad Afzal, 35, told an AFP correspondent at the scene. A security official said the suicide bomber's face and head were found at the scene "but most of his body has been torn into pieces".

Hundreds of people were inside the building at the time of the blast, the correspondent said. "There is blood everywhere in the mosque and outside it. Human limbs are scattered all over the mosque compound."

The attack will raise fears that Taliban militants, who continue to wage a guerrilla revolt in southern and eastern Afghanistan, are further stepping up a renewed onslaught which has left more than 250 people dead this year.

In a separate bomb attack Wednesday, two Afghan mine clearance workers were killed by a remote-controlled roadside bomb in the neighbouring southern Afghan province of Helmand.

The US military, which leads an international coalition of 18,300 troops hunting remnants of the Taliban, condemned the Kandahar attack and offered to help Afghan authorities in the aftermath.

"The coalition abhors this atrocious act of violence upon innocent civilians and a mosque," US Army Colonel Jim Yonts, a spokesman for the coalition, said in a statement. "Tragic events such as this only solidify our resolve that we must eradicate terrorism now. The future of Afghanistan depends on it."

The Taliban claimed responsibility after two armed men on a motorcycle on Sunday gunned down cleric Fayyaz, who was chief of Kandahar's Islamic Council. Fayyaz organized a meeting of other Afghan Islamic clerics in Kandahar last week in which the council of ulemas, or scholars, revoked the title of Amirul Mominine, the leader of all believers, given to Mullah Mohammed Omar.

Two years ago a bomb exploded in the same mosque, which is named after the cleric's father, wounding Fayyaz and 23 others. Kandahar has been hit by other previous bombings, including twin roadside blasts on March 17 that killed five people and wounded more than 30 while US Secretary of State Condoleezza Rice visited Kabul. On Monday up to 16 militants and four police officers were killed in a series of attacks in southern Afghanistan.