A powerful suicide bomb attack on a bus in the Afghan capital, Kabul, has killed at least 27 members of the country's armed forces, officials say.

The bus was split in two by the blast and witnesses described seeing several dead bodies around the wreckage.

The Taleban claimed the attack, Kabul's second deadliest since 2001.

Responding to the attack, Afghan President Hamid Karzai said he wished he could ask insurgent leaders why they were trying to destroy the country.

In June, a police bus was targeted in Kabul, killing 35 officers in the worst attack in the city since the fall of the Taleban.

Windows shattered

Defense ministry spokesman Gen Zahir Azimi told the BBC that a further 21 people were injured in the bus blast.

He said a man dressed in army uniform detonated an explosive device as he climbed on to the bus.

More than 3,000 people have been killed this year as Afghan and foreign forces battle Taleban fighters.

The BBC's Alastair Leithead, in Kabul, says the sound of emergency sirens has been ringing across Kabul since early in the morning after the blast.

The head of the Kabul police, Gen Alishah Paktiawal, said the bomb went off at 0630 (0200 GMT) on board a bus packed with army staff.

"For 10 or 15 seconds, it was like an atom bomb - fire, smoke and dust everywhere," a police officer who witnessed the explosion told the Associated Press.

The bus was ripped apart in the blast, and windows in nearby houses were shattered.

President Hamid Karzai said he wished he could contact Taleban leader Mullah Omar and warlord Gulbuddin Hekmatyar to ask why they were trying to destroy Afghanistan.

He said he would meet both men personally, and even offer them cabinet posts, if it would help to bring about peace.

When similar offers have been made in the past, the militants have insisted talks could take place only if foreign forces left Afghanistan.

President Karzai once again reiterated he would not agree to any troop withdrawal.

PHOTO CAPTION

President Hamid Karzai