A suicide bomber has struck a Shia mosque in Pakistan's garrison city of Rawalpindi, killing seven people and wounding several others, police have said.

Police told Al Jazeera that the attacker blew himself up when he was stopped at the gate of the mosque.

The blast occurred as minority Shias gathered in the mosque to distribute alms to mark the birthday of the Prophet Muhammad.

Witnesses said the explosion was powerful and blew out windows.

Tehreek-e-Taliban Jamaat-ur-Ahrar, a faction of the Pakistani Taliban, claimed responsibility for the attack. 

'United against terrorism'

Pakistan Interior Minister Chaudhry Nisar condemned the attack and declared an emergency in all hospitals in the Rawalpindi area. 

"These kinds of attacks cannot break the will of the people of Pakistan. The whole nation is united against terrorism," he said in a statement.  

Police said a team investigating the incident would present a report in 14 days. 

Security has been beefed up around Rawalpindi and Islamabad following the attack.

The area where the blast took place is home to several Shia mosques and residential buildings and was the site of tensions in November 2013, when an altercation between Sunni protesters and Shias during a Shia Ashoura procession turned into full-blown riots, resulting in the deaths of several people.

Taliban fighters and al-Qaeda have targeted the country's Shia minority in the past.

A bomb targeting Shia at a volleyball match killed at least four people and injured eight in Pakistan's restive northwest last Sunday.

The incident happened at the Hussaini ground, owned by the local Shia community in the Kalaya neighbourhood of the Orakzai tribal district.

Pakistan has strengthened its own offensive against the Taliban since their attack on a military-run school on December 16 killed 150 people, 134 of them children.

Source: Al Jazeera and agencies