At least 10 people have been killed in a suicide bombing in the central Afghan province of Uruzgan, officials say.
Many of those killed were civilians in a crowded market 500 metres from the governor's office in provincial capital Tarin Kowt. Dozens more were hurt.
A man claiming to speak for the Taleban said the group carried out the attack.
The bomber's target is unclear. US ambassador Ronald Neumann was in the governor's office at the time of the blast but was unhurt, officials said.
US embassy spokesman Lou Fintor said Ambassador Neumann had returned to Kabul.
"The ambassador and his party are safe and have been accounted for. They were not in any danger," he told the Associated Press.
President Hamid Karzai, on a visit to Turkey, said the attack had been carried out by the "enemies of peace".
'Screaming and crying'
It is unclear whether the attacker meant to blow himself up in the market, or if his bomb went off prematurely as he headed towards the governor's office.
Uruzgan's deputy governor Haji Abdul Aziz said it did not appear to have been a car bomb, as earlier reported.
"We need to wait for the investigation results but it seems now that the suicide bomber had strapped explosives to his body," he told the AFP news agency.
"Fifteen of the wounded are in critical condition, including the provincial police director. The area was crowded because the US ambassador was visiting."
The most seriously wounded have been taken to hospital in the nearby city of Kandahar.
November 2005: 3 civilians killed in Kandahar
September 2005: 12 killed outside Afghan army base in Kabul
May 2005: 3 killed in Kabul internet cafe
June 2005: 20 killed in Kandahar mosque
October 2004: 3 killed in Kabul shopping centre
August 2004: 10 US security contractors killed in Kabul
Witnesses in the market spoke of scenes of carnage.
"People were lying dead and wounded everywhere. They were screaming and crying," one man told AP.
Deputy governor Aziz told the BBC that the governor, Jan Mohammad Khan, was not present for the talks with the US officials.
He is currently in Mecca in Saudi Arabia for the Hajj, the annual Muslim pilgrimage.
Taleban spokesman Qari Mohammad Yousuf said a local man, who he named as Abdul Rahim, had carried out the attack. He gave a number of different media organisations varying accounts.
Thursday's blast was one of the deadliest in a series of suicide attacks in Afghanistan in recent months.
The upsurge in attacks comes as the US plans to hand more responsibility for security in Afghanistan to Nato allies.
Afghan officials say they suspect Taleban and other militants opposed to the US-backed government in Kabul may be importing tactics used by insurgents in Iraq.
Local intelligence officials say they believe a large number of foreign militants recently infiltrated Afghanistan to join the campaign being waged by the Taleban, whose leader Mullah Omar comes from Tarin Kowt.
Attacks linked to insurgency, mostly in southern and eastern Afghanistan, left more than 1,400 people dead in 2005 - the country's bloodiest year since US-led forces ousted the Taleban in late 2001.