A homicide attacker on a motorbike detonated a bomb Wednesday outside an Afghan military training center in Kabul (search), killing nine soldiers and wounding 28 other people, the Defense Ministry said.

The attacker struck in a parking lot where officers and soldiers of the Afghan National Army (search) were waiting to take minibuses home at about 4 p.m. A purported Taliban spokesman claimed responsibility and threatened more homicide attacks.

It was the deadliest bombing in the Afghan capital in at least a year and breaks 10 days of calm after landmark parliamentary elections. Those polls were relatively peaceful despite Taliban threats of violence.

The U.S.-trained Afghan National Army is a key plank of international efforts to rebuild the country after decades of war and factional strife.

President Hamid Karzai (search) condemned the attack in "the strongest terms" as he ordered an investigation.

The commander of the training center, Gen. Ghulam Saki, said the bomber killed nine army personnel. The 28 people treated in a military hospital included three civilians.

Defense Ministry spokesman Gen. Mohammed Zaher Azimi said the attack appeared to be the work of a homicide bomber. He blamed "international terrorists" but did not elaborate.

Homicide attacks are far less frequent in Afghanistan than in Iraq.

Khail Mohammed, an Afghan soldier who witnessed the attack, said a uniformed man on a motorbike, believed to be the attacker, drove into the parking lot of the Kabul Military Training Center on the Jalalabad Road in the city's eastern section as the buses were preparing to leave.

"I saw the bodies of badly mutilated soldiers and the buses were on fire," he said.

In the aftermath, an Associated Press reporter saw three blackened, badly damaged minibuses, one lying on its side. Investigators examined the blast site under mobile floodlights, while NATO peacekeepers searched nearby woods with flashlights.

NATO troops, U.S. soldiers and Afghan police blocked roads to the area.

In a call to The Associated Press nearly five hours after the attack, purported Taliban spokesman Mullah Latif Hakimi said the bomber was an Afghan Taliban known as Mullah Sardar Mohammed.

Hakimi's account of the attack seemed at odds with witness accounts. He claimed the attacker struck at the headquarters of the Afghan army as foreign instructors were training Afghan cadets.

He said other Taliban fighters were ready to launch homicide attacks on U.S.-led coalition and Afghan government forces.

Information from Hakimi in the past has sometimes proven exaggerated or untrue. Afghan and U.S. military officials say he is believed to speak for factions of the rebel group, though his exact ties to the Taliban leadership cannot be verified.

Outside the military hospital, about 30 wailing and shouting relatives waited for news of loved ones.

"I condemn this brutal action of the terrorists in our country. They are against human beings," said Shaukat, a 23-year-old who gave only one name.

Fighting back tears, he said he had heard that his cousin, an army officer, had been wounded, but soldiers would not let him past the hospital gates to try to find him.

The attack underscores the terrorist threat in Afghanistan four years after U.S.-led forces ousted the hard-line Taliban regime for hosting Usama bin Laden and his Al Qaeda network.

The Sept. 18 elections were viewed as a key step in the country's transition toward democracy after two decades of war and civil strife, but many outlying areas in the south and east remain prey to Taliban-led insurgents. The capital, patrolled by NATO peacekeepers, is regarded as relatively secure.

The last major explosion in Kabul was in August 2004, when a car bomb tore through the office of a U.S. security contractor that provided security for Karzai, killing about 10 people. The Taliban claimed responsibility.

There has been an upsurge in violence this year in the south and east. More than 1,300 people, many of them rebels, have died in the past seven months. Senior Afghan officials also have spoken of Al Qaeda operatives entering the country to stage attacks.

On June 1, a homicide blast in the southern city of Kandahar during the funeral of a moderate Muslim cleric critical of the former Taliban regime killed 20 people, including the Kabul police chief, and wounded 42.

That attack stoked fears that insurgents fighting the Afghan government and U.S.-led coalition forces were copying deadly tactics used in Iraq.