KABUL, Afghanistan (Washington Post) – President Hamid Karzai narrowly escaped an assassination attempt in the southern Afghan city of Kandahar Thursday evening, just three hours after a powerful car bomb exploded in a crowded street in downtown Kabul, the capital, killing at least a dozen people and injuring scores more.

No one had claimed responsibility for either attack as of late Thursday night, and Afghan officials said that they knew of no links between the two, which were among the worst incidents of violence since the defeat of the Taliban militia and the installation of the U.S.-backed Karzai government late last year.

But the officials said they had been expecting terrorist activity with the approach of two anniversaries of violent events that had a major impact on Afghanistan: the assassination of anti-Taliban militia leader Ahmed Shah Massood last Sept. 9 and the terrorist attacks in New York and at the Pentagon two days later. Both incidents were blamed on Osama bin Laden’s al-Qaida organization, which was based in Afghanistan during the Taliban’s five years in power.

“The leaders of Taliban and al-Qaida are on the run, they are struggling for survival, they are trying to show their organizations are not fully destroyed,” Foreign Minister Abdullah said Thursday night. “This just strengthens our committment and determination in the war against terrorism, and it is further evidence that the war against terrorism is far from over.”

Although the bombing in Kabul was the more spectacular and lethal of the day’s attacks, the attempt on Karzai shook the government far more deeply. The president, 44, is the virtually the only national leader in fractious postwar Afghanistan; efforts to end factional fighting and to rebuild a crippled economy are largely identified with him, and there is no formal plan to replace him in an emergency.

Karzai, who was in Kandahar for a family wedding, had just stepped into a car outside the provincial governor’s office when a uniformed gunman opened fire directly in front of the vehicle, officials said. Karzai was uninjured, but Gov. Gul Agha Sherzai, a passenger in the same vehicle, was wounded in the neck, A U.S. Special Forces soldier guarding Karzai recieved “minor injuries” in the attack, according to the U.S. Central Command in Tampa, Fla., and was in stable condition after being treated near Kandahar.

Karzai has been protected by U.S. Special Forces since shortly after the assassination of Vice President Abdul Qadir on July 6 in Kabul. The U.S. troops replaced a security detail from the Afghan Defense Ministry and security agencies, which are controlled by Karzai’s political rivals.

Large crowds turned out to greet Karzai Thursday in Kandahar, the heartland of his Pashtun ethnic group. His car was in a heavily guarded convoy, and he had leaned out of his window to greet an Afghan boy when the unidentified gunman began shooting, according to news reports. U.S. Special Forces guards leapt from a jeep in the convoy and fired back, killing the assassin and two other people. Abdullah said an Afghan guard was also killed.

Afterward, Karzai spoke to reporters at the governor’s guest house, saying: “I’m fine. I expect things like this to happen.”

The attack took place at 6:30 p.m., and when the news reached Kabul, the city of 2 million was already reeling from the massive mid-afternoon explosion, which left an entire city block covered with shattered glass and bloodstains and sent thousands of panic-stricken people fleeing in cars and on bicycles from the crowded city center.

The impact of the bomb, planted in a parked taxi, was especially devastating because it detonated in a narrow street in the heart of downtown that was filled with shoppers making purchases before the weekly Friday Muslim holiday, and because the device detonated just moments after a smaller bomb exploded on a bicycle nearby, drawing many onlookers to the scene.

The second explosion shattered windows in dozens of shops, offices and a hotel across the street, leaving dozens of bystanders with wounds from hurtling glass shards. Trails of bloody footprints led from the spot where the taxi and several other parked cars were charred black. Sidewalk vendors’ stalls were reduced to rubble, with crushed vegetables, sandals and cigarette packs strewn on the pavement.

“I heard the first explosion and I went to the door to look. Then I heard a louder one and saw a big fire. People were lying on the street and screaming for help,” said Najeeb Shahabi, 28, a California resident who was visiting his father’s electronics shop a few feet from the blast. “It was a terrible experience. I want to go home to the States, and I think I won’t come back.”

The wounded were loaded into taxis and rushed to half a dozen nearby hospitals, where doctors and survivors said between 80 and 100 people were treated for injuries. At least 10 were confirmed dead, but officials said Thursday night that the death toll was rising because many of the injuries were serious.

Wayed Ahmad, a businessman from Kandahar who was staying at the Spinzar Hotel, was eating lunch when he heard the first explosion and got up to see what had happened. The second blast blew out the hotel windows, driving glass into his arms and legs.

“I couldn’t tell if it was day or night,” said Ahmad, 35, whose knee-length Afghan tunic was drenched in blood as he emerged from Kabul’s military hospital with a bandaged arm. He said he had been taken there in an ambulance with 15 of the other wounded. “I can’t say who did this, but it is a very sensitive time for Afghanistan, and this will hurt the progress of the country and the government.”

Police stopped and searched hundreds of vehicles all afternoon and evening, causing massive traffic jams, but no one had been arrested by late Thursday night, and no one claimed responsibility for the bombing. Thousands of people with grim and worried faces hurried on foot from the area, which is two blocks from a teeming central market and one block from two government ministries.

“This is the work of terrorists, of al-Qaida. It is a crime against Islam, against Afghanistan, against humanity,” said Khalil Aminzada, a city police official at the bomb scene. “These groups were defeated, but now they are showing their terrible face again. If we do not destroy them, these things will keep happening.”

Several smaller explosions have occurred in Kabul since mid-August, including one bomb left at the Telecommunications Ministry, another inside a movie theater and a third next to a U.N. guest house. Those blasts caused little damage and few injuries, and officials described them as warnings or harrassment from unknown groups.

But Thursday’s bomb was clearly aimed at inflicting serious harm and sowing public panic in the capital, which is heavily patrolled by about 4,500 members of an international peacekeeping force while the fledgling government trains a national police force and army.

Some officials and witnesses speculated that the twin attacks were timed to coincide with the two anniversaries of the violent attacks last September, especially with preparations for a series of public memorials for Massood, a national hero who fought against Soviet occupation and Taliban rule and was killed by a bomb in northern Afghanistan one year ago.

There were also suggestions that Gulbuddin Hekmatyar, the renegade former Islamic militia leader and onetime Afghan prime minister, might have been behind the attacks. Afghan and foreign military officials said they believe Hekmatyar, an ethnic Pashtun, may have formed an alliance with the remnants of Taliban and al-Qaida forces still hiding in the border areas of Afghanistan and Pakistan.

Hekmatyar, who has been a fugitive since March and has called for a “holy war” against U.S. forces here, issued a taped message two days ago that called for Afghans to rise up against the government and its foreign backers. “All true Muslim Afghans who want an Islamic government … must know it is possible only when the United States and allied soldiers are forced out. We must all unite and rise against them,” Hekmatyar said on the tape, delivered to news offices in Peshawar, Pakistan.