Taliban militants detonated a suicide bomb and stormed a bank in southern Afghanistan on Wednesday, killing at least six people as the country endures a rise in violence while U.S.-led NATO troops pull out.

The attackers forced their way inside after the bomb exploded at the entrance of the Kabul Bank branch in Lashkar Gah, the capital of the insurgency-racked province of Helmand.

"The blast at the gate was a suicide attacker blowing himself up to open the way for others to enter the building," Omar Zhwak, provincial spokesman for Helmand, told Agence France Presse.

"The fighting is still ongoing. Our latest report show six people, including three police, have been killed and seven wounded.

"One attacker was also killed and two are still resisting.

"It was the government employees' payday and they had all come to get their salaries."

Farid Ahmad Obaidi, Helmand's police spokesman, confirmed the incident, which comes as Afghanistan police and army take over security duties nationwide.

Officials were unable to confirm if any civilians were trapped inside the branch.

A Taliban spokesman claimed responsibility for the attack on Kabul Bank, an institution that nearly collapsed in 2010 in a $900 million fraud case that underlined endemic corruption in Afghanistan.