Gunmen have attacked and entered a Pakistan air force base, according to Reuters.

The target is the Minhas Air Base in the town of Kamra, located around 40 miles outside Islamabad. The attacked is believed to be conducted by the Tehreek-i-Taliban Pakistan (TTP) — reports in the Pakistan press have suggested they were planning attacks in retaliation for upcoming military action.

A three hour gun battle is reportedly raging between security guards and attackers.

Time Magazine's Omar Waraich points out that this is the third attack on the base since 2007.

Worryingly, the militants may have good reason to attack the base. Waraich says that the site is home of Pakistan's nascent drone program, and a Telegraph report from 2009 said the site was thought to house Pakistan's nuclear weapons. Saeed Shah wrote at the time:

Pakistan’s nuclear sites are tightly guarded. While experts do not think that terrorists could seize an actual nuclear bomb — the weapons are not kept in a useable form, with parts dispersed — it is possible that they could cause a fire or explosion inside a nuclear site, or perhaps seize radioactive material.

UPDATE: 2 soldiers and 6 militants have been left dead from the fighting, Reuters reports.