Kandahar, Afghanistan ? An assailant dressed in the uniform of the new Afghan army fired Thursday on a car carrying President Hamid Karzai, hours after an explosives-packed car tore through a crowded Kabul market, killing at least 10 people.

The violence was the most serious challenge to Karzai’s government, which has been struggling to bring order and security to a country wracked by decades of bloodshed.

Debris and wreckage litter the busy market area of Kabul, Afghanistan. A powerful car bomb was detonated Thursday in the center of the Afghan capital, in the bloodiest attack in Kabul since the fall of the Taliban. Hours later, an assailant fired on a car carrying Afghan President Hamid Karzai.

Afghan officials were quick to blame Osama bin Laden’s al-Qaida network for the violence, which came less than a week before the anniversary of the Sept. 11 attacks.

“Terrorists are behind both attacks, there is no doubt about it. And terrorists in this region are led by Osama and his associates,” Foreign Minister Abdullah said.

The government offered no immediate evidence of bin Laden’s involvement, and others blamed the rising anger of the Pashtun majority toward a government controlled by Americans and dominated by rival Tajiks from the north.

The British Broadcasting Corp. said the attacker came from a former Taliban stronghold.

President Bush expressed relief that Karzai was safe, and administration officials pledged to keep helping rebuild the country.

“We’re not leaving,” Bush said. “We want to help democracy flourish in that region.”

The assassination attempt occurred soon after Karzai, who was in his hometown of Kandahar for the wedding of his youngest brother, finished evening prayers at the city’s historic Khalqa Sharif mosque.

Afghan President Hamid Karzai speaks near a mosque in Kandahar just before an assassination attempt. Karzai survived the assault Thursday when an Afghan security guard fired at his car as it was leaving the governor's mansion in Kandahar, witnesses said.

After the prayers, Karzai and his party were given a tour of the governor’s mansion, located across the street from the mosque. Karzai’s motorcade was preparing to leave the governor’s compound as hundreds of well-wishers were pressing against the gates to catch a glimpse of the president.

“We were standing at the gates and saw Karzai wave,” said Sardar Mohammed. “Then I saw one guard point a Kalashnikov at Karzai and fire. There was a kid behind him, and he grabbed the gunman from behind.”

Kandahar security chief Dur Mohammed said Karzai’s U.S. military bodyguards immediately opened fire, killing the assailant and two others. The presidential motorcade sped off within moments of the attack, while gunsmoke lingered over the mansion’s grounds. The governor of Kandahar, Gul Agha Sherzai, was grazed in the neck; Karzai was unharmed.

In its report, the BBC identified the attacker as Abdul Rahman, who had joined the security forces of Sherzai less than three weeks ago.

The BBC said he was from Kajaki in the province of Helmand, an ethnic Pashtun region west of Kandahar. Helmand is one of the areas where U.S. forces searched for the fugitive Taliban leader Mullah Mohammed Omar.

After the attack, Karzai returned to the governor’s compound, where he is staying, and said he was fine.

BBC reporter Lyse Doucet, who was with the president at the time of the attack, said that as crowds were pressing toward the president, an Afghan boy approached his vehicle. When Karzai leaned out to shake hands with the boy, “an Afghan in uniform also came forward and fired two rounds into the president’s vehicle.”

Shortly afterward, reporters saw three bullet-riddled bodies all relatively young men with trimmed beards sprawled at the front gates, covered with traditional Afghan shawls. One was in uniform, while the others were dressed in civilian clothes. Their assault rifles were nearby.

The assassination attempt occurred hours after a car bomb rocked a busy market area in the center of Kabul, the bloodiest attack in the Afghan capital since the fall of the Taliban late last year.

There was confusion over the death toll in Kabul. Police said 10 people were killed. Afghan state television put the number of dead at 26 with 150 injured. The Italian Emergency Hospital said 65 people were admitted.