KABUL, Afghanistan - A suicide bomber detonated his explosive vest yesterday at a military base in eastern Afghanistan, killing eight Americans, U.S. officials said.

The explosion occurred at Forward Operating Base Chapman in Khost province near the Afghan border with Pakistan.

State Department spokesman Ian Kelly confirmed that eight Americans died.

"We mourn the loss of life in this attack, and are withholding further details pending notification of next of kin," he said.

In Kabul, a spokesman for the international coalition force in Kabul said that no U.S. or NATO troops were killed in the afternoon explosion at Chapman, one of dozens of forward operating bases that support reconstruction efforts and other civilian operations across the nation.

An attacker wearing a suicide vest caused the explosion, according to a senior U.S. official in Washington. Another senior U.S. official in Washington said that there were conflicting reports on the number of casualties but that others were injured in the attack. The officials spoke on condition of anonymity.

Angry protests

Wazir Pacha, a police spokesman in Khost province, said that local people reported hearing a blast on the base where an explosion in January killed an Afghan civilian and wounded four others. Soon afterward, two helicopters landed, a police officer in Khost said.

In another attack, NATO said that four Canadian troops and a journalist from Canada were killed yesterday in an explosion in Kandahar province. The journalist was traveling with the troops on a patrol.

Separately yesterday, NATO questioned Afghan reports that international troops killed 10 civilians, including schoolchildren, in a weekend attack that prompted hundreds of angry Afghan protesters to burn an effigy of President Obama and chant "death" to America.

The head of an investigative team appointed by Afghan President Hamid Karzai said by telephone that eight students between the ages of 12 and 14 were among the dead discovered in a village house in a remote section of Kunar province in eastern Afghanistan.

NATO said in a statement released late last night that while there was no direct evidence to substantiate the claims, the international force had requested and welcomed a joint investigation.

Resentment

Conflicting accounts of what occurred during fighting in Kunar's Narang district prompted an emotional outcry over civilian deaths, one of the most sensitive issues for international troops fighting the more than eight-year-old war.

Although insurgents are responsible for the deaths of far more civilians, those blamed on coalition forces spark the most resentment and undermine the fight against extremists. With 37,000 more U.S. and NATO troops being deployed, concern over civilian casualties is unlikely to ease anytime soon.

Several hundred Afghans demonstrated in the capital of Kabul and in the eastern city of Jalalabad, where the likeness of Obama, adorned with a small American flag, burned on a pole held above demonstrators.

In Kabul, protesters carried signs that read: "Does peacekeeping mean killing children?" and "Stop killing us." A protester with a bullhorn called on Obama to "take your soldiers out of Afghanistan."