A homicide bomber targeted Shiite Muslims on two buses being escorted by security forces through a northwestern Pakistan border area rife with sectarian and insurgent violence, killing 12 people Friday.

Tensions between Pakistan's majority Sunni Muslims and Shiites had made the road unsafe for the minorities traveling to the nearby Kurram tribal region. Police recently had declared it safe, but Shiites are provided security to travel through it.

Friday's attack only targeted the buses carrying Shiites, police official Akram Ullah said. Security forces escorting them weren't harmed.

The victims were passing through a gas station in the town of Hangu when the lone attacker on foot set off the bomb, Ullah said.

Five people were killed at the scene and seven others died at hospitals, he said.

Pakistan's northwest has been plagued for years by Islamist extremist violence fueled by anger over the war in Afghanistan and Islamabad's alliance with Washington. An army offensive that began in October against the Pakistani Taliban spurred attacks that killed more than 600 people.

But with the exception of a few attacks on northwest police stations, violence appears to have subsided in recent weeks, an indication that the army operation in the South Waziristan tribal region may be having an impact.

Sectarian tensions are another matter.

Extremist Sunnis and Shiites have targeted each other's leaders in violence that dates from well before the 2001 terrorist attacks in the United States.

Several of Pakistan's Sunni extremist groups also are allied with the Taliban and al-Qaida, who view Shiites as infidels. The Sunni-Shiite schism over the true heir to Islam's Prophet Muhammad dates to the seventh century.

Also Friday, Pakistan army helicopters destroyed a sprawling hideout of a key al-Qaida-linked militant leader, Maulvi Faqir Mohammed, in the northwestern tribal region of Bajur, killing 25 insurgents.

However, it was unclear whether Mohammed was present at the time, according to an army and intelligence official. The officials spoke on condition of anonymity because they were not authorized to speak to media.

Mohammed is a close aide to al-Qaida No. 2 leader Ayman al-Zawahri.

He is also the deputy chief of Tehrik-e-Taliban Pakistan, an umbrella organization of several militants whose chief, Hakimullah Mehsud, is believed to have died in an American missile attack near the Afghan border in January.

The Pakistani Taliban have denied Mehsud's death.

On Sunday, they released a video of Mehsud, but his taped comments fail to prove he survived the missile strike.