Militants armed with machine guns and suicide vests attacked one of Pakistan's largest air force bases pinning down security forces for more than two hours and raising new concerns about the safety of the country's nuclear arsenal.

Though official Pakistani sources denied it, the Minhas base north of Islamabad is believed by some to house some of the nation's 100 or so nuclear warheads. Even if it doesn't, the group that launched a late night raid on the facility may have believed that it did. At least nine attackers stormed the base around 2:00 a.m. local time, firing rocket propelled grenades from outside the base gates, before climbing the walls and engaging security guards in a firefight that lasted at least two hours. All nine attackers were eventually killed, with one exploding a suicide bomb.

The assault may also been a preemptive strike meant to disrupt the government's operations in North Waziristan.  The New York Times reports the Pakistan military was preparing to launch an operation on the Taliban and al Qaeda strongholds in that region. Whether or not any of Pakistan's sensitive weapons were ever in danger, the attack is still an embarrassment for the Pakistani military, which seems unable to control the threat of militant attacks and had trouble containing such small force.

The AP also reported just hours later that 20 Shiites Muslims were pulled off of buses in Northern Pakistan and murdered, though it's unclear who is responsible or if the two attacks could be related.