KABUL, Afghanistan – A powerful car bomb exploded early Tuesday within a few feet of a passing military convoy on the western edge of Kabul, killing at least a dozen Afghan civilians and six foreign troops, including five Americans, U.S. military and Afghan officials said.

The radical Islamist Taliban movement claimed responsibility for the blast, which it said was carried out by a suicide bomber driving a vehicle packed with 1,650 pounds of explosives.

The blast overturned a heavy military truck and gouged an enormous crater in a street near the ruined Darulaman Palace, once home to Afghanistan’s royal family, witnesses said. Five vehicles in the convoy were heavily damaged, along with more than a dozen civilian cars and a public bus.

It was the first major bombing in the Afghan capital since February, and one of the deadliest in recent memory for the troops of the International Security Assistance Force (ISAF).

A U.S. military spokesman said five of the troops killed were Americans, and the Canadian government said one of its service members also died, the Associated Press reported.

The Afghan Interior Ministry reported that at least 12 Afghan civilians were killed and 47 wounded in the bombing, which occurred about 8 a.m. when people were on their way to work. Many of the civilian victims had been waiting at a nearby bus stop on the busy road that runs past the former palace and government ministries.

The attack was condemned by ISAF officials and by Afghan President Hamid Karzai, who recently returned to Kabul following a visit to Washington.

In Washington, White House deputy press secretary Bill Burton said in a statement, “While our troops are fighting for a better future for the Afghan people, the Taliban offers only destruction, and they have so little respect for humanity that they would murder Afghan civilians waiting for a bus.”

The U.S. and Afghan governments “remain steadfast in our determination to build security, stability and opportunity for Afghanistan,” Burton said.

“This sort of desperate brutality and aggression reminds us of the pessimism of an enemy who seeks to kill the innocent and to stop the progress of securing a better future for this country,” said Brig. Gen. Josef Blotz, an ISAF spokesman.

NATO Secretary-General Anders Fogh Rasmussen said the attack would not deter the alliance from its mission to “protect the Afghan people and strengthen Afghanistan’s ability to resist terrorism.”

The bombing occurred during preparations for a “peace jirga” organized by the Karzai government to try to reconcile the country’s warring factions and pave the way for an eventual withdrawal of international troops.

One week ago, a Taliban group issued a statement warning of “ambushes, detonations of explosive devices, assassinations of government officials, suicide bombings and detainment of foreign invaders.”

Until Tuesday, the worst Taliban attack in the capital occurred on Feb. 26 when armed assailants stormed a pair of guest houses used by Indian nationals, killing 17 people.

More than 200 ISAF soldiers have been killed in Afghanistan this year.