Ambulances and police rushed to the scene of the attack
A suicide car bomb has exploded outside the Nato headquarters in the Afghan capital, Kabul, killing up to seven people, the defence ministry says.
The presidential palace and several embassies are also located in the area.
The attack comes ahead of presidential and provincial elections due on Thursday which the Taliban have vowed to disrupt.
The BBC's Martin Patience says a group affiliated to the Taliban is likely to be responsible for the attack.
President Hamid Karzai condemned the attack, saying people would not be deterred from voting.
"The enemies of Afghanistan try to create fear among people in this election period but people still realise the importance of going to ballot boxes to cast their votes," he said in a statement.
Initial reports said three people, all Afghan civilians, had been killed and 70 people injured.
The Afghan defence ministry issued a statement later saying that it believed seven people had been killed.
The blast hit the heavily fortified area of the city at about 0830 local time on Saturday.
Ian Pannell, BBC News, Kabul
This is one of the most heavily guarded streets in Kabul. You have to go past huge concrete blast walls. There are men with guns almost everywhere, Afghan forces, international forces. There are barriers and chicanes. It is not an easy area to get into.
Security sources are telling us there isn't enough co-ordination between the different security agencies, the Afghan security forces, the police, the special forces and the international forces and that has created a real sense that they are not on top of the security situation.
It is very surprising the attackers were able to get into this area. Normally you have to show a pass, the car is looked at, the passengers are questioned. But it seems they were able to get past the first checkpoints and approach the Nato headquarters where the bomb exploded.
"It was a suicide bombing carried out in a car right in front of Isaf [the Nato-led peacekeeping force]," Afghan defence ministry spokesman General Mohammad Zahir Azimi said, speaking from the scene.
Several Isaf soldiers were among the injured.
Sirens blared as police and ambulances rushed to the area which was sealed off by international forces.
"As I was walking into the Nato compound I heard a loud explosion and fell to the ground," one man, Ahmad, told the BBC.
"People were screaming and I saw flames from the headquarters. We all left the area, as we were worried there might be a second bomb."
One of the injured was the female MP Hawa Alam Nuristani, who is also working for President Karzai's election campaign.
Some of those taken to hospital have been undergoing surgery to treat severe wounds.
The BBC's Martin Patience in Kabul says that, while there is an elaborate security plan to try to keep violence to a minimum ahead of the elections, there will be real concern that there will be more attacks in the city in coming days.
He says that attacks inside the capital are relatively rare but have tended to be big ones.
The last major attack on the capital was in February when several gunmen, some wearing suicide vests, attacked the Ministry of Justice.
In July 2008, a massive car bomb killed more than 50 Afghans and two diplomats outside the Indian embassy.
These two attacks were believed to have been carried out by a group called the Haqqani network, our correspondent says.
It is named after the veteran Afghan militant Jalaluddin Haqqani, who is based in Pakistan's North Waziristan region. He is an old man now and the group is led by his son, Sirajuddin Haqqani.
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