A suicide car bomber killed at least nine people in an attack on a military airport in eastern Afghanistan on Monday, officials said, the latest incident of violence and protests since copies of the Koran were inadvertently burned at a NATO base last week.

There was no official indication the explosion at the gates of Jalalabad airport was linked to other deadly protests and riots, although the Taliban quickly claimed responsibility for the attack as 'revenge' for the Koran burning.

Anti-Western fury has deepened significantly since the desecration of the Muslim holy book at the main NATO base in Afghanistan.

Twelve people were wounded by the suicide bomb at the airport and casualties appeared to be civilians and Afghan soldiers who were guarding the gate, the Interior Ministry said in a statement.

A spokeswoman for the NATO-led International Security Assistance Force (ISAF) in Nangarhar province, of which Jalalabad is capital, said the explosion did no damage inside the military airport, which is used by ISAF troops.

Riots have raged across Afghanistan over the past week despite widespread apologies from U.S. leaders, including President Barack Obama and military commanders.

On Sunday, seven U.S. military trainers were wounded when a grenade was thrown at their base in Afghanistan's north.

Chants of 'Death to America' have been common at protests and some demonstrators have raised the white Taliban flag.

With few signs of the crisis abating, the U.S. ambassador to Afghanistan said the United States should resist the urge to pull troops out of Afghanistan ahead of schedule.

"Tensions are running very high here. I think we need to let things calm down, return to a more normal atmosphere, and then get on with business," Ambassador Ryan Crocker told CNN's 'State of the Union' in an interview from Kabul.

"This is not the time to decide that we are done here. We have got to redouble our efforts. We've got to create a situation that al Qaeda is not coming back," he said.

Under an international agreement, foreign combat forces are due to leave Afghanistan by the end of 2014, a process which is already underway.

WIDESPREAD ANGER

The groundswell of anger over the burning of the Koran, which Muslims revere as the literal word of God, has highlighted the challenges ahead as Western forces try to quell violence and bring about some form of reconciliation with the Taliban.

The protests have killed more than 30 people and wounded at least 200, including two U.S. troops who were shot dead by an Afghan soldier who joined rallies in the east.

In an interview from Rabat, U.S. Secretary of State Hillary Clinton said the violence "is out of hand and it needs to stop".

The shooting at close range of two U.S. officers deep inside the heavily fortified Interior Ministry in Kabul on Saturday has intensified the sense of unease among Westerners and deepened the divide with their Afghan counterparts.

The attack illustrates the dilemma faced by NATO forces as they move away from a combat role to an advise-and-assist mission, which will require them to place more staff in Kabul's ministries.

With the 2014 timetable unfolding, pressure is growing for an earlier pullout, especially among Washington's allies in Europe, where the bloody and expensive war is deeply unpopular.

The high-level killings prompted NATO, Britain and Germany to withdraw their staff from Afghan ministries.

The Taliban also took responsibility for the Interior Ministry attack, although the Islamist group often exaggerates claims involving attacks against Western forces.

On Sunday, the ministry said one of its employees was a suspect in the shooting of the two U.S. officers.

Afghan security sources also identified Abdul Saboor, a 25-year-old police intelligence officer, as a suspect in the shooting of the Americans at close range inside the interior ministry. The ministry said the suspect had fled.

CCTV footage showed that Saboor had access to the Command and Control Centre, tucked deep inside the ministry, where the slain Americans were found, security officials said on condition of anonymity.

Afghan President Hamid Karzai has repeatedly urged calm and restraint in the face of bloody protests, although he also maintains that those who burned the Korans must be prosecuted.

In Washington, a U.S. Defense Department spokesman said the Afghan defense and interior ministers were postponing scheduled trips to the United States this week to talk with other Afghan leaders about how to protect ISAF troops and quell the violence.

The United States is by far the largest contributor to the NATO-led force in Afghanistan, which is gradually ceding security responsibility to Afghans.

Under an agreement reached at an international conference in Lisbon in December 2010, the NATO force is to wind down its combat operations by the end of 2014, although there are signs that process may be hastened.

Earlier this month, U.S. Defense Secretary Leon Panetta suggested the United States could end its combat role as early as next year, remarks that surprised allies in Europe and Kabul.

Similar incidents of desecration of the Koran in the past have also sparked violence, although not as widespread and persistent as the riots and protests over the past week.

Last April, seven foreign U.N. staff were killed when protesters over-ran a base in the northern city of Mazar-i-Sharif after an obscure pastor from a fringe church in the United States deliberately burned a copy of the Koran.