Pakistani volunteers move an injured worshipper near a Shia Muslim mosque after an attack there by Taliban militants in Peshawar on Friday.

AFP/Islamabad

Grenade-toting Taliban militants stormed a Shia mosque in northwest Pakistan on Friday, police said, in an attack that left at least 18 people dead.

The incident comes two weeks after a suicide bombing at a Shia mosque in southern Pakistan killed 61 people, the deadliest sectarian incident to hit the country in nearly two years.

Police said several gunmen threw grenades before storming the Imamia mosque in Peshawar, the main city in Pakistan's restive northwest, around the time of the main Friday prayers.

An AFP reporter saw 18 bodies in the Hayatabad Medical Complex, while the hospital's public relations officer Toheed Zulfiqar put the toll at 19, saying one of the dead may have been an attacker.

The Tehreek-e-Taliban Pakistan (TTP) claimed responsibility for the attack in an email statement.

Senior police official Mian Saeed said the assault, which left more than 60 wounded, began when the militants entered the mosque from a nearby building site.

"They were wearing suicide vests and carrying grenades and Kalashnikovs," Saeed said.

"One blew himself up while another was shot by police and was later killed. The operation inside the mosque is over but we are conducting a search operation in the surrounding buildings," he said.

TV footage showed people running away from the scene, some carrying injured on their shoulders, others limping, as police fired shots and checked people at a barrier.

Witness Muhammad Raza said: "There was a huge explosion, I can see many injured lying in front of me."

An AFP reporter at the scene saw soldiers and police commandos arriving.

The mosque is close to several government buildings including the offices of the Federal Investigation Agency and passport agency.

Mushtaq Ghani, information minister for Khyber Pakhtunkhwa province, of which Peshawar is the capital, told Geo TV the attack was a response to the army's ongoing offensive against militants in the tribal areas along the Afghan border.

Since June last year the army has been waging a major campaign against strongholds of Taliban and other militants in the North Waziristan tribal area, which lies close to Peshawar.

The country has stepped up its fight against militants since a Taliban school massacre in Peshawar in December.

Heavily armed gunmen went from room to room at the army-run school gunning down more than 150 people, most of them children, in an attack that horrified the world.