
The insurgents targeted the US Provincial Reconstruction Team (PRT) facility in Rokha district, Panjshir province, killing two drivers and leaving two guards wounded, said provincial police chief Mohammad Qasim Jangalbagh.
The police and the governor's office confirmed that it was the first suicide attack in the Panjshir valley since the war began, underscoring the violence being wrought on once-tranquil parts of the country after a decade at war.
The Taliban claimed responsibility, saying the attack was launched with a car bomb packed with 600kg of explosives. The rebel group frequently exaggerate their claims.
Security for the ethnic Tajik-dominated area once ruled by guerrilla hero Ahmad Shah Massoud was handed over from Western troops to Afghans in July.
"An explosion which targeted the PRT in Panjshir left two drivers dead and two guards of the PRT wounded," said Jangalbagh.
He said the drivers had been bringing fuel supplies to the base when it came under attack.
"The first suicide attacker detonated his explosives inside his four-wheel drive vehicle while the other three reached the PRT gate and exploded themselves," he said.
"The Americans are inside their base, and the bodies of the suicide attackers lie at the gate of the PRT," he added.
A spokesman for the NATO-led International Security Assistance Force (ISAF) Christopher Pewitt confirmed the incident but had no record of fatalities.
"We can confirm a suicide attack on the PRT early this morning in Panjshir. There were no casualties to ISAF. Civilians were injured in the blast," he said, without giving further details.
Taliban spokesman Zabihullah Mujahid said the insurgents attacked the gate of the base.
"Five mujahedeen fighters attacked the gate of PRT in Panjshir province and detonated a car packed with 600kg of explosives," he told AFP by phone from an undisclosed location.
Afghan political analyst Mahmood Saikal said the insurgents' ability to strike in the heart of one of the most peaceful provinces "undermines the security transition process".
"How did these suicide attackers enter that province, because we have had good security in Panjshir province?" he said.
Violence across the country was up by nearly 40 percent in the first eight months of this year compared to the same period last year, according to UN figures that are disputed by ISAF.
ISAF claims instead that attacks were down two percent over the same period.
Elsewhere Saturday, two Taliban insurgents died and three others were wounded when mines they were assembling exploded in the restive southern province of Kandahar, senior local officials said.
The men were making the bombs in a tent in Dand district, said provincial government spokesman Zulmai Ayoubi.
"As a result of the explosion two were killed and three wounded," he said, adding that the toll may rise.
"They were killed by their own mines," confirmed Kandahar police chief Abdul Razeq.
Roadside bombs are the weapon of choice for the Taliban, whose 10-year insurgency has been largely focused on the southern heartland.
The United Nations says the first half of this year saw 1,462 civilians killed, with insurgents responsible for 80 percent of the deaths.
There are 140,000 foreign forces in Afghanistan, some 100,000 of them from the United States, fighting to reverse the Taliban-led insurgency.
All combat troops are due to leave by the end of 2014 when Afghan forces take over full responsibility for security although thousands are likely to remain in training and mentoring roles.
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