Militants have attacked traffic police headquarters in the west of the Afghan capital, Kabul.
Two explosions went off outside the office just before dawn, injuring some civilians and police, officials said.
Gunmen then attacked the building and Afghan forces are now trying to dislodge two militants holed up inside.
The Taliban, who have hit a number of Kabul targets recently, claimed responsibility for the attack in a text message sent to media organisations.
Last week the group attacked the National Directorate of Security in the city centre, killing four guards working for the intelligence services.
The two militants still inside the huge traffic police complex are armed with heavy machine guns and rocket-propelled grenades, and have been tossing hand grenades out of windows of the third floor, reports the BBC’s Bilal Sarwary in Kabul.
Police were trying to prevent them getting on to the roof of the four-storey building.
The attack began when at least one militant blew himself up outside the headquarters, police said.
A powerful car bomb also went off and a second attacker was shot by security forces.
Explosions could be heard across the city and black smoke could be seen rising from the upper floors of the building.
Earlier, Kabul Police head General Ayoub Salangi told the BBC that four police and six civilians had been wounded in the attack.
Our correspondent says the strategic location of the traffic department – close to several key police units as well as the country’s parliament – suggests it could have been chosen as a launching pad for a more prolonged attack.
The incident was causing traffic gridlock in certain areas of Kabul – where busy intersections are controlled by police rather than traffic lights – as officers were unable to get to work.
Militant groups continue to mount regular attacks in Afghanistan, raising questions as to how the Afghan security forces will cope after international troops leave the country in 2014.
On Monday, Afghans took to Twitter and Facebook to criticise the security services for their inability to prevent such audacious insurgent attacks.