At least five explosions have been heard in Afghanistan's eastern city of Jalalabad, with heavy gunfire also reported at a police headquarters close to the provincial governor's office, sources told Al Jazeera.

Jalalabad's police commissioner said 11 people were killed in Thursday's attack, including 10 policemen and one civilian, with a further 14 police officers injured, two of whom are in a serious condition.

At least five attackers were also killed, sources said. The Taliban has claimed responsibility for the attack.

Seven suicide bombers were involved in the attack, one of whom used a car bomb, and six others used explosive vests, the police commissioner also said.

Al Jazeera's Jane Ferguson, reporting from Kabul, said the attack started around 5:30am local time in District One of Jalalabad and that the ensuing gun battle lasted for more than four hours.

"The police headquarters came under attack after five huge explosions hit the city," she said.

The headquarters is in one of the safest parts of the city, near the provincial governor's house,.

Sources told Al Jazeera that "gunmen with suicide vests entered the police station" while 12 police officers were on duty.

The country is preparing for elections on April 5 and the Taliban has vowed to disrupt the polls.