Several Taliban suicide attackers tried to storm a US military base in eastern Afghanistan early Tuesday and at least six have been found dead, a provincial governor said.

NATO's International Security Assistance Force confirmed that a US military base in the eastern town of Khost, 30 kilometres (19 miles) from the border with Pakistan, was under attack but could give few details.

"We have heard about suicide bombers on foot. They are receiving indirect fire," an officer in the ISAF media office in Kabul told AFP.

He could not give details because fighting at Camp Salerno was ongoing, he said.

The Khost governor, Arsala Jamal, said several men had tried to attack the base.

"According to our reports about 30 Taliban tried to attack the Salerno base. They were fired at. We have found six bodies which were all wearing suicide vests," he told AFP.

"Some of them have blown themselves up. Others are hiding in nearby houses and corn fields. The troops are searching for them," he said.

Four Afghan army troops had been wounded in the fighting, the governor said.

The attackers had also launched rockets at the base, an Afghan army officer told AFP on condition of anonymity.

The new attack comes a day after a suicide bombing outside Camp Salerno killed 10 Afghan labourers and wounded 13 more.

Security forces were able to prevent a second suicide attack moments later, the US-led coalition and Afghan officials said. The Taliban claimed responsibility.

  
A secretary to the Khost governor, Mohammad Bilal, gave the same same toll. "It was a suicide car bombing against the gates of the Salerno camp," he said.
  
"Moments later a second car bomber came and wanted to detonate his bombs. Police identified him and opened fire on him," Bilal added.
  
He said the attacker was able to escape into the crowd and security forces destroyed the second bomb. "They wanted to disturb Independence Day."
  
The dead and wounded were labourers who had been waiting to enter the base for work, provincial government spokesman Khaibar Pashtun said.
  
Reacting to the suicide bombing, Karzai said in a statement that by killing "innocent civilians on Independence Day, the terrorists showed their hostility to the freedom of Afghan people."
  
The Al-Qaeda-linked Taliban were driven from power in a US-led invasion in late 2001.
  
However they were able to regroup, some of them taking refuge in Pakistan, to launch a snowballing insurgency which military officials say is attracting more Arab, Pakistani and other Muslim fighters.
  
The coalition and separate NATO-led International Security Assistance Force helping Afghanistan fight the extremists issued a rare warning of a "heightened security threat based on credible intelligence reporting."
  
"These reports indicate that the enemies of the people of Afghanistan intend to attack civilian, military and government targets during Afghan independence celebrations," a statement said.
  
UN staff were told to stay at home while other international personnel were told to restrict their movements.
  
"Staff are working at home as precaution," UN spokesman Aleem Siddique told AFP.
  
The capital has suffered a series of attacks in recent weeks.
  
The education minister escaped a roadside bomb Saturday, while two separate blasts in the city this month have killed two foreign soldiers and about seven Afghans.
  
The last major parade in the capital Kabul, on April 27, was disrupted when militants opened fire on a stage where Karzai, ministers, diplomats and other senior officials were seated.
  
Karzai survived but three people as well as three of the attackers -- said to be from the Taliban militia -- were killed.
  
In other violence reported Monday, a mine blew up a police vehicle in the province of Nangarhar and killed two policemen, an official said.
  
Meanwhile, the coalition said it had killed several militants on Sunday in separate operations in Paktia and Kapisa provinces. It did not give a number.