Kabul, Afghanistan (CNN) -- Nine Americans, including four U.S. troops, were among those killed in a suicide bombing in Afghanistan's capital this weekend, a western diplomat told CNN Sunday.
Saturday's blast -- which also claimed the lives of two British civilians, a Kosovo national and a Canadian soldier -- occurred when a car packed with explosives struck an armored bus in a NATO convoy, the diplomat said.
Confusion over casualties arose because some people on board the bus were not listed on its passenger manifest, the diplomat said.
Afghan officials said four Afghans, including two students, were also killed.
A senior NATO official described the bus as a custom-built, heavily armored Rhino.
Canadian Master Cpl. Byron Greff was among the dead, according to the Canadian Expeditionary Force Command.
Authorities have not released identities of the other victims. A diplomatic source said the two British citizens who were killed were civilian contractors working for ISAF.
Afghan President Hamid Karzai offered his sympathies at a national security meeting Sunday.
"Afghan people are grieved by the NATO loss of lives and share the pain and sorrow with the families and friends of the troops killed," he said.
A Taliban spokesman confirmed Saturday's attack in a text message, saying it killed "16 foreign soldiers, one civilian" and injured many others.
Taliban casualty counts are often inflated; there was no other reliable indication 16 foreigners were killed.
It was unclear how many people were wounded, said Sediq Sediqqi, an Interior Ministry spokesman.
The U.S. Embassy in Kabul expressed condolences to families and said it will continue the victims' "dedicated work on behalf of peace in this country and region."
"It's a shock. It makes you mad. It makes me angry," said U.S. Ambassador Ryan Crocker. "We are not going to let these guys win."
The attack was one of several targeting NATO-led forces Saturday.
About 27 people were killed in clashes between troops and suspected insurgents in Nangarhar province, east of Kabul, ISAF said in a statement.
Attackers fired rocket-propelled grenades and small arms at coalition troops who were assisting Afghan forces at the site of a land dispute, the statement said. No ISAF forces were injured or killed, the statement said.
The fighting erupted after the Taliban convinced members of a tribe that they should attack a convoy carrying government officials to reclaim their land, said Haji Lewani, a tribal elder in the province. About 20 Taliban insurgents and seven tribesmen were among the dead, he said.
Also Saturday, a gunman wearing an Afghan army uniform turned his weapon on coalition forces during training, killing three and wounding several others, ISAF said. The shooter was killed in the incident in southern Afghanistan.
The coalition did not provide any other details about the shooting, and did not disclose the nationalities of those killed.
Nearly 2,800 troops from the United States and its partners have died during 10 years of war in Afghanistan, according to a CNN count.
CNN Pentagon correspondent Barbara Starr and journalist Ruhullah Khapalwak contributed to this report.