Taliban gunmen with suicide bombs and heavy weaponry on Tuesday launched coordinated attacks in Kabul targeting NATO's headquarters and the US embassy, killing at least six people.

Around five hours after the attack began, gunbattles still raged. The Afghan government confirmed the deaths of four civilians and two policemen, plus at least six insurgents, with at least two militants still resisting after dusk.

Afghan officials said attackers were hunkered down in a multi-storey building under construction that overlooks the NATO headquarters and US embassy, exchanging fire with security forces as two helicopters flew overhead.

Two separate suicide attackers also targeted police in some of the most heavily protected parts of the capital, with the Taliban insurgency at its deadliest since US-led troops ousted the Islamists' regime 10 years ago.

Any simultaneous attacks that succeeded in hitting NATO headquarters and the US embassy would be the Taliban's most ambitious commando-style operation yet in their fight to evict the Kabul government and defeat Western troops.

In any case, the attacks dealt a humiliating blow to the Afghan government and NATO, underscoring worsening security in Kabul, where insurgents have staged increasingly brazen commando-style raids on Western and Afghan targets.

AFP reporters heard a string of loud blasts shortly after 1:30 pm (0900 GMT) just two days after the United States marked the 10-year anniversary of the 9/11 attacks that triggered the long war in Afghanistan.

The US-led International Security Assistance Force (ISAF) works with diplomatic missions to prop up an Afghan government increasingly seen as corrupt. Its main headquarters is adjacent to the US embassy compound.

"ISAF HQ is under attack at the moment," a Western military official earlier confirmed as terrified residents and shopkeepers told how they dived for cover.

The US embassy -- one of the largest American diplomatic missions in the world, one of the most heavily protected compounds in Afghanistan and home to hundreds of diplomats -- confirmed only an attack "in the area".

"There are no casualties at this time among embassy personnel," added spokeswoman Kerri Hannan in an emailed statement, providing no further details.

An Afghan interior ministry official, speaking anonymously, said four policemen and two civilians were killed.

Officials said at least five civilians and three policemen were wounded. A journalist from Afghan state broadcaster RTA was shot and wounded during the standoff, an AFP reporter said.

"Security forces have reached the second and third floor (of the multi-storey building," said police spokesman Hashmat Stanikzai.

"Two (of the attackers) are still resisting. We hope their resistance will end soon. They have almost run out of ammunition," he added.

ISAF confirmed it was providing "air support" although NATO chief Anders Fogh Rasmussen had said he was confident that Afghan forces, who officially control security in Kabul, could deal with the assault.

Afghan officials said the suicide attacks targeted police, one near parliament and both in the western part of the capital.

They said three insurgents were killed at the building and another on the airport road with seven kilos of explosives, although details were unclear.

That would suggest that up to nine attackers were involved in the assaults.

A Taliban spokesman told AFP by text message that the targets were ISAF headquarters, the US embassy and Afghanistan's intelligence agency, the National Directorate of Security (NDS) and other "sensitive government places".

"Today at one o'clock at Kabul's Abdul Haq roundabout a massive suicide attack on local and foreign intelligence facilities is ongoing," wrote Zabiullah Mujahid in the text message to AFP.

The ISAF headquarters in Kabul oversees the operations of the bulk of the estimated 140,000 foreign troops fighting the Taliban in Afghanistan.

"I was sitting in my shop when suddenly I heard an explosion and then another one. Then there was gunfire," said Abdulbaqi, a local shopkeeper.

"People on the streets started running. I had to leave my shop to get to safety," he added.

Officially Kabul is under the control of Afghan security forces, along with most of its surrounding province and six other parts of the country handed over by NATO-led troops in July as part of a staggered, timetabled withdrawal.

President Hamid Karzai insisted the attacks would not derail the transition process but would "rather embolden our people's determination in taking the responsibility for their country’s own affairs".

But last month, nine people died when suicide bombers attacked the British Council in Kabul.

In June, Taliban militants also stormed the luxury Intercontinental Hotel in Kabul, sparking a fierce battle that left at least 12 people dead.

The US military has blamed some of the worst attacks on the Al-Qaeda-linked Haqqani network, whose leadership is based in neighbouring Pakistan and enjoys the protection of Pakistani intelligence agents.