-- A suicide bomber wearing an army uniform blew up a motorcycle packed with explosives near Afghan troops boarding minibuses outside their base in Kabul on Wednesday afternoon, killing nine men and injuring 28, Afghan authorities and witnesses said.

A purported spokesman for the Taliban militia, Abdul Latif Hakimi, claimed that a Kabul resident named Mullah Sardar Mohammad had carried out the attack on behalf of the insurgency. Gen. Mohammed Zahir Azimi, a spokesman for the Ministry of Defense, said authorities were still investigating who was behind the blast, one of the deadliest in the city since the Taliban regime was ousted by U.S.-led forces in 2001.

The attack renewed concerns that the insurgents are turning to tactics more common to Iraq, where suicide bombings against local troops are frequent.

Also Tuesday, a U.N. worker from Bangladesh and an Afghan government employee were injured when their vehicle hit a land mine on a road under construction in eastern Nangahar province, according to provincial and U.N. officials.

Since this spring, suspected Taliban insurgents have mounted a series of ambushes and roadside bombings throughout the south and east. The guerrillas did not follow through on threats to disrupt parliamentary elections Sept. 18, but U.S. military officials have warned that they may carry out significant attacks throughout the fall.

Despite the upsurge in violence, bombings in Kabul, which is patrolled by a NATO-led force in addition to Afghan police, have been relatively rare. The most recent major explosion occurred in August 2004, when suspected Taliban militiamen set off a car bomb at the office of a U.S. security firm, killing about 10 people.

Wednesday's bombing occurred about 4:30 p.m. in front of the Afghan National Army's training camp on the main road leading east out of Kabul.

Lt. Col. Abdulbaqi Ashana, an army instructor in his late thirties who was reached by phone in Kabul's main military hospital, said the blast occurred shortly after he had taken his seat on one of three minibuses.

He said he looked out the window and saw a man in an army uniform slowly wheeling a motorcycle between two buses.

"I thought, 'Why is that person pushing that motorcycle?' " Ashana recalled. "Then suddenly there was a very harsh sound. I saw black smoke and that was it."

Ashana, who suffered shrapnel wounds in one arm, said he and others rushed out of the bus toward a medical clinic on the base, from which they were evacuated by ambulances.

Some relatives who managed to reach other survivors by phone said they had painted a grisly picture of the bombing's aftermath, describing one bus as incinerated and piled with charred corpses.

NATO and Afghan troops quickly arrived at the site, closing off the road to all traffic while a German ordnance disposal team searched the area. About 100 relatives of victims, unable to reach the base, massed for several hours in front of the military hospital, desperate for news.

"Yes, that's right, Najibullah has been missing since the explosion," Khalil Ahmad, 35, muttered into a cell phone as he paced by the hospital entrance, seeking news of his brother. "I don't know if he's dead or alive. They won't tell us anything."

Next to him, Najibullah Ahmad's 13-year-old son wiped tears from his eyes.

A hospital doctor said most of those killed were army officers. Since its formation in 2002, the Afghan army has grown to about 25,000 troops. It is a key component of a plan to reduce the number of U.S. troops here from about 20,000 today to between 14,000 and 16,000.

Norwegian troops close a road on Kabul's outskirts after a suicide bomber blew up a motorcycle near Afghan troops.