Taliban gunmen with suicide vests and rocket-propelled grenades have launched coordinated attacks targeting the US embassy and NATO headquarters in the heart of the Afghan capital Kabul.

Militants carried out a series of attacks, setting off a number of explosions across the city and firing rocket propelled grenades and automatic weapons from a partially constructed high-rise building in the diplomatic quarter.

Up to six people have been killed in the fighting so far and this morning the gunmen were still exchanging fire with security forces, more than 10 hours after the battle began.

The US embassy blared out warnings for staff to take cover as the insurgents struck on Tuesday afternoon (local time).

Suicide bombers also targeted police in other parts of the city. A school bus was hit by a rocket during heavy fighting in the neighbourhood of Wazir Akbar Khan, but witnesses said there were no students on the bus at the time.

Afghanistan correspondent Sally Sara says the main attacks were on the US embassy and the headquarters of the NATO-led International Security Assistance Force (ISAF), where up to six gunmen took control of the high-rise.

The attacks again highlighted poor security in Kabul, where insurgents have staged a string of increasingly brazen commando-style raids on Western and Afghan targets in recent months.

The Afghan government has condemned the violence.

Security breached

Battle: Afghan security forces at the scene of the fighting ( Massoud Hossaini: AFP )

US secretary of state Hillary Clinton vowed that the "brave" Americans who work at the embassy would not be put off by such attacks.

"They will not be intimidated by this kind of cowardly attack," she said.

"We will take all necessary steps not only to ensure the safety of our people but to secure the area and to ensure that those who perpetrated this attack are dealt with."

The giant, high security US embassy compound borders the ISAF compound where thousands of foreign troops live and work.

ISAF spokesman Lieutenant Colonel Jimmie Cummings said there had been no casualties among its personnel, who are trying to support the Afghan government in efforts to reverse Taliban momentum.

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

A Taliban spokesman said 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".

Witnesses told of their terror as the attacks unfolded.

"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."

ABC/wires