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The BBC's Quentin Sommerville in Kabul: "We've heard multiple explosions" 

Afghan and international security forces are battling an ongoing multi-pronged attack by insurgents targeting the US embassy, Nato headquarters and police buildings in Kabul.

Police are still exchanging fire with two gunmen holed up in an unfinished high-rise building overlooking the diplomatic quarter.
Six people have been killed and 16 injured, Kabul's police chief said.
The Taliban said they were behind the violence.
Police killed four insurgents, police chief General Ayub told the BBC.
"This attack is the work of the Haqqani network," he said. The Haqqani network is closely allied to the Taliban, but operates independently.
Gen Ayub said the insurgents wanted to carry out attacks in Kabul to coincide with the 10th anniversary of 9/11.
Nato said the attack was an attempt to derail the security handover to Afghan-led forces, as international troops begin to withdraw from Afghanistan.
Co-ordinated attack Tuesday's attacks appear to be a complex operation. At about 13:30 local time (09:00 GMT), insurgents fired rockets on a number of targets in Kabul's upmarket embassy district. At the scene

Quentin Sommerville BBC News, Kabul

The Taliban have shown consistently that they can attack right at the heart of the Afghan government and the international mission.
It does not matter how secure those buildings are, the insurgents are still managing to cause chaos in the city.
The Taliban have already issued a statement saying that at least four suicide attackers are involved in this assault on government ministries and the intelligence headquarters in this district.
As well as reports that insurgents have taken refuge in a high-rise building overlooking the entire area, we are also getting reports that there may be another two attackers wandering the streets, so people have taken cover.

In the west of the city, another two suicide attackers detonated explosives outside a police station.

A third was killed as he tried to make it into the airport. A jail run by the intelligence service was also a target.
Six gunmen took over an unfinished high-rise building near the Abdul Haq roundabout, overlooking the embassy district, and used it to fire on the Nato compound and US embassy.
A Taliban spokesman said the group was carrying out "a massive suicide attack on local and foreign intelligence facilities".
Nato and the US embassy said none of their staff were among the casualties of the attack.
US marines were seen on the roof of the embassy building assessing the situation and checking their defences were robust, correspondents say. Military helicopters are in the area.
Nato's Secretary General Anders Fogh Rasmussen condemned the violence, describing it as an attempt to test the handover of Afghanistan's security to Afghan-led forces, an effort that would not succeed.
"We have confidence in the Afghan authorities' ability to deal with this situation," said Mr Rasmussen in Brussels. "Transition is on track and it will continue."
Twisted metal One witness, Mohammad Zada, said he was driving past the US embassy building when the attack started, adding that he heard five explosions.

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Eyewitness Himanshu Sharma describes the scene from his office in Kabul

"Nothing really prepares you for shards of twisted metal, scattered glass, victims and the debris that litters the streets," said Mr Zada, who works for Agility Global Integrated Logistics in Kabul.
Video footage showed a group of men taking shelter from gunfire - one with blood pouring from his arm - as sirens wailed through the city.
Another eyewitness, Himanshu Sharma, told the BBC: "I thought it would be over in a few minutes, but then one hour and then two hours and then three hours passed - it was just not stopping.
"The gunshots were increasing, and their intensity was increasing. They were using more deadly weapons."
He went on: "There is no security at all in Kabul. This is the safest area, and if we are not safe here, then we are not safe anywhere in Afghanistan. "

Recent Kabul attacks

• August 2011: Gunmen storm British Council HQ, killing 12 people
• June 2011: Seven people killed in gun and bomb attack at Intercontinental Hotel
• April 2011: Two soldiers killed after gunman opens fire inside defence ministry
• Jan 2011: Eight killed by suicide bomber at Kabul Finest supermarket
• Feb 2010: At least 17 people killed in gun and bomb attack on foreign guesthouse district
• Jan 2010: 12 dead in attack on government targets and shopping malls