Fighting erupted in the volatile east Afghanistan city of Khost today, security officials and witnesses said, with at least three suicide bombers attacking government buildings.
The US military had heard reports of attacks by suicide bombers in Khost and was investigating but had no further details, a spokeswoman for US forces in Kabul said.
US and Afghan forces are battling a growing Taliban-led insurgency in the east.
Interior Ministry spokesman Zahir Azimi said a car packed with explosives had been detonated in Khost city, followed by three suicide bombers. He said details were still unclear but sporadic fighting was continuing.
A statement by the Ministry of Defence said "a group of suicide bombers" had attacked government offices in Khost and three had blown themselves up, causing "casualties and damage".
Salahuddin Ayubi, a spokesman for the al Qaeda and Taliban-linked Haqqani network, said a suicide car bomber had attacked a district government building in the city, blowing open the gates to allow gunmen and more suicide bombers to enter.
He said they had inflicted "heavy casualties".
A Reuters reporter in the city heard at least two loud blasts but there was no immediate confirmation of casualties.
The Haqqani network has mounted similar attacks against Afghan government and US military targets in the past.
The latest attacks followed a similarly brazen pattern to assaults by Taliban gunmen and suicide bombers, some dressed as women, on the eastern city of Gardez in neighbouring Paktia province on Tuesday. Nine people were killed.
Would-be suicide bombers also attempted attacks in Jalalabad near the border with Pakistan the same day.
Violence this year had already reached its worst levels since the Taliban were ousted by US-backed Afghan forces in 2001.
Attacks across the country have escalated further since thousands of U.S. Marines and British troops launched major new offensives in the southern province of Helmand, long a Taliban stronghold, early this month.
The offensives are the first under US President Barack Obama's new regional strategy to defeat the Taliban and its militant Islamist allies and stabilise Afghanistan.
In May, four suicide bombers blew themselves up in Khost, killing at least six people, and gunmen laid siege to government buildings, holding hostages for a time, before they were overpowered.Reuse content