Seven Taliban fighters with rocket-propelled grenades and machine guns launched a rare assault on NATO's operational headquarters at the military section of Kabul's international airport on Monday. All seven militants were killed.

Their failed attack showed that despite an asphyxiating security blanket around the capital, Afghanistan's insurgency is far from defeated after nearly 12 years of war, and militants can still menace the capital.

Gunfire and explosions from the pre-dawn battle could be heard in many parts of Kabul. No one was killed except the attackers, but it emphasized the challenges faced by Afghanistan's fledgling security forces as they prepare to take the lead from a U.S.-led coalition that is rapidly withdrawing its remaining forces.

The spectacular attacks are aimed at demoralizing the population and sowing mistrust in the Afghan security forces' ability to protect their citizens — rather than military gains.

"We can expect high profile attacks, we can expect insider threats and we can expect maybe some assassinations," said German Gen. Gunter Katz, spokesman for the U.S.-led International Security Assistance Force.

"We adapt our security measures appropriately, we assess the security situation on a permanent basis and we remain very vigilant."

The Taliban, who claimed responsibility for the airport attack, have been testing Afghan security forces as foreign combat troops pull back more than a decade after the U.S.-led invasion to oust the Taliban regime for sheltering al-Qaeda's leadership after the Islamic extremist group launched the Sept. 11, 2001, terrorist attacks in the United States.

In declaring their spring campaign, the Taliban said they would target Afghan and coalition forces and government officials around the country. Although they said they would not target civilians, the overwhelming number of dead and wounded so far has been ordinary Afghans.

The attack was one of three against state facilities on Monday morning by insurgents around the country.

In addition to the airport attack, six militants wearing suicide bomb vests tried to storm the provincial council building in the capital of southern Zabul province, while three attempted to attack a district police headquarters near the capital. Elsewhere, a roadside bomb killed a Polish soldier in the NATO force.

Not close to aircraft

Interior Ministry spokesman Sediq Sediqi said that in Zabul the attackers wounded 18 people, including three police officers, when they detonated a car bomb outside the building in the city of Qalat, but security forces shot and killed them before they could enter. On the outskirts of Kabul, police killed one attacker and arrested two others who tried to storm the headquarters building in the Surobi district.

At the airport, the insurgents did not get close enough to attack aircraft and were not near the runway's flight path. Even if they had managed to damage the airport, it would have affected civilian flights but not had an impact on military operations, which are carried out from a military airfield at Bagram about 50 kilometres (30 miles) north of the capital.

But they did manage to sneak in a minivan full of explosives, rocket-propelled grenades, heavy machine guns and assault rifles along with their suicide vests. Such weapons have been used repeatedly in Kabul attacks over the recent months, including an eight-ton bomb on a truck in March that was discovered just before it was to be used to attack a NATO base.

'Cowardly terrorist attacks'

Afghan President Hamid Karzai said his government would not be deterred.

"These cowardly terrorist attacks on the Afghan people cannot change the chosen path of the Afghan people toward progress, development, peace and elections," Karzai said, referring to next spring's poll to elect a new head of state.

Karzai was not in Kabul during the attack, but was visiting the Gulf state of Qatar, where he was discussing his country's stalled peace process and the possible opening of a Taliban office in Doha.

Both Afghanistan and the United States support the opening of a Taliban political office in Qatar as part of an effort to rekindle talks with the insurgent group. But first, Kabul and Washington say, the Taliban must renounce all ties to al-Qaeda and other terrorist groups and accept Afghanistan's constitution.

Sediqi said the attacks are motivated by the upcoming handover of the lead for security from the U.S.-led coalition to the Afghan army and police. Afghan forces are now leading 90 per cent of the military operations in areas where 80 per cent of the country's population lives. After the handover later this month, the coalition will assist, train and mentor, providing military support only in emergencies.

The 352,000-strong force numbered less than 40,000 six years ago. The coalition will shrink by half its current 97,000 troops at the end of this year.

"Of course, in the coming days, there will be a transition and security is going to be handed over to Afghan forces," Sediqi said.

No runway damage

"They are trying to sabotage that process and trying to bring the ability of the Afghan security forces into question, which they cannot because today's incidents in three different parts of the country were all foiled without significant casualties."

The Kabul airport itself was not damaged and reopened shortly after the fighting was over, said airport chief Yaqub Rassuli.

"There was no damage to the runway. Some shrapnel fell nearby, but we have cleared it away," Rassuli said.

Deputy Kabul police chief Dawood Amin said two insurgents blew themselves up with suicide vests at the start of the assault and five were shot and killed by police during the battle.

The last major incident in Kabul was May 24, when six suicide bombers attacked a UN-affiliated group, killing three people. On May 16, a suicide bomber rammed a car into a NATO convoy, killing 15 people, including two American soldiers and four civilian contractors.