KABUL, Afghanistan (AP) — A suicide bomber detonated his vehicle near a U.S. convoy Tuesday, killing 18 people, including six troops — five Americans and a Canadian — in the deadliest attack on NATO in the Afghan capital in eight months.

Two other American service members were killed in separate attacks in the south, making Tuesday the deadliest day of the year for U.S. forces in Afghanistan.

The Canadian, Col. Geoff Parker, 42, was the highest-ranking member of the Canadian Forces to die in Afghanistan since the Canadian mission began in 2002, the country’s military said.

Twelve Afghan civilians also died — many of them on a public bus in rush-hour traffic along a major thoroughfare that runs by the ruins of a one-time royal palace and government ministries. At least 47 people were wounded, the Interior Ministry said.

The blast was the first major attack in the Afghan capital since February and followed a Taliban announcement of a spring offensive even as the U.S. gears up for a major push to restore order in the turbulent south.

Taliban spokesman Zabiullah Mujahid claimed responsibility for the blast, telling The Associated Press in a telephone call that the bomber was a man from Kabul and that the vehicle was packed with 1,650 pounds (750 kilograms) of explosives.

Afghan President Hamid Karzai joined the U.S. and NATO in condemning the attack, which he said killed women and children.

The explosion, which thundered across the capital, happened about 8 a.m. as streets were packed with cars, buses and trucks. The bomb ripped apart vehicles and hurled body parts along the street. U.S. and Afghan forces blocked off the area as emergency workers loaded the wounded into ambulances.

“I saw one person lying on the ground with no head,” said Mirza Mohammad, who was on his way to work when the blast took place. Police officer Wahidullah, who goes by one name, said he saw the body of a woman in a pale blue burqa smashed up against the window of the bus.

“Dead bodies were everywhere,” Wahidullah said.

U.S. forces spokesman Col. Wayne Shanks said five American service members were killed in the Kabul blast. That plus the two deaths in the south brought the number of U.S. troops killed in Afghanistan, Pakistan and Uzbekistan since the war began in 2001 to at least 994, according to an Associated Press count.

The Kabul attack was the heaviest loss of life for NATO in a single attack in the capital since Sept. 17, when a suicide car bomber killed six Italian soldiers. For U.S. forces, it was the bloodiest day since Oct. 27, when nine Americans died in separate attacks in central and southern Afghanistan.

Earlier this month, the Taliban announced a new offensive — “Operation Al-Fatah” or “Victory” — which would target NATO forces, foreign diplomats, contractors and Afghan government officials.

The announcement was made on the eve of Karzai’s visit to Washington and comes as U.S., NATO and Afghan forces are gearing up for a major operation to secure Kandahar, the biggest city in the south and the former Taliban headquarters before they were ousted from power in the 2001 U.S.-led invasion. U.S. officials believe control of Kandahar is the key to stabilizing the Taliban’ southern heartland.

Kabul has been abuzz for weeks with rumors of imminent Taliban attacks against Afghan government and international targets. The last major assault in the city occurred on Feb. 26 when suicide attackers struck at two residential hotels, killing six Indians and 10 Afghans.

Afghan authorities blamed the February attack on Lashkar-e-Taiba, the Pakistan-based militant group that India blames for the 2008 Mumbai terrorist attacks that killed 166 people.

On April 8, Afghan police announced they had arrested five would-be suicide bombers on their way to carry out a major attack in the city. Eleven days later, the Afghan intelligence service said nine members of a terrorist cell had been arrested — presumably from the support network that was to have helped the five others carry out their attacks.

The bombing Tuesday suggests the Taliban have reconstituted their underground cells, presumably from within the city’s large Pashtun community which forms the bulk of the insurgent force.

Also Tuesday, Afghan and NATO aircraft continued the search for an Afghan commercial airliner which disappeared Monday on a flight from Kunduz to Kabul with 44 people on board, including three British citizens and an American. Air traffic controllers lost track of the Antonov-24, operated by Pamir Airways, when it was about 55 miles (85 kilometers) north of Kabul.

“Right now, we are looking to identify the location of the crash,” Karzai said at a news conference. “In some areas, the bad weather — snow, rain and fog — will not let us do the search. We’re very hopeful that we will able to find the victims of the crash soon and hand the bodies over to their families.”

Abdul Shakour, a district official in Parwan province, said seven tribal elders in the area where the plane was last reported each promised to send two or three experienced climbers to search the remote mountains for any sign of the missing aircraft.

For families of those aboard the aircraft, however, despair turned to anger over delays in finding the wreckage.

“People are very upset with the government because it has no forces here to help us. And these 48 countries in ISAF, where are they today? They are not here to help us,” said Mohammad Isahq, a Kabul shopkeeper whose nephew, Omar Sahel, was a flight attendant on the plane.

Isahq said that the families were ready to do the search themselves if authorities would provide them with proper equipment and point them in the right direction.

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Associated Press writers Heidi Vogt in Kabul, Jamey Keaten in the Salang Pass and Slobodan Lekic in Brussels contributed to this report.

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