A least six people have been reported killed in a Taliban attack on an Afghan intelligence building in the eastern city of Jalalabad, sources have told Al Jazeera.

The attack early on Saturday began with a suicide car bomb. Security forces battled with an unknown number of Taliban fighters for an hour before authorities were able to put down the attack.

"The attack was carried out by a vehicle bomb on the Nangarhar provincial National Directorate of Security (NDS) office, and then some militants started attacking the office," Ahmad Zia Abdulzai, spokesman for the Nangarhar provincial governor, told the AFP news agency.

He would not say how many attackers were involved or whether they were all killed or some escaped. He said authorities were searching the grounds.

Hospital officials told Al Jazeera that at least six people have been killed in the attack, and 45 wounded. Both civilians and members of the military are among the dead.

Taliban spokesman Zabihullah Mujahid claimed responsibility for the attack, claiming several NDS agents were killed in the attack.

The intelligence service has regularly been targeted by the Taliban.

In December 2012, NDS head Asadullah Khalid was seriously wounded in an attack by a Taliban "envoy" who detonated an explosive device hidden in his underwear.

Jalalabad is one of Afghanistan's biggest cities, sitting on a major trade route into neighbouring Pakistan. But the city is also located in one of the country's most troubled regions.

The Taliban have stepped up attacks on symbols of power in recent weeks, seeing to destabilise the fragile Afghan state which is in the midst of a political crisis over the appointment of a new president to succeed Hamid Karzai, who has led the country for 13 years.