Pakistani police say militants are attacking one of their stations in the northwestern part of the country, killing at least seven police officers.

Local police officials said at least seven militants armed with guns and grenades launched their attack on a station in the small town of Kolachi. At least 17 police officers were on duty at the time.

By late Saturday, officials said the attack was ongoing and security forces had been called to the scene.

Kolachi is located near Pakistan's volatile South Waziristan tribal region, a known stronghold for the Pakistani Taliban and an area where the Pakistani military is targeting militants.

While no one immediately claimed responsibility for the attack, the Pakistani Taliban has vowed retaliation for the killing of al-Qaida leader Osama bin Laden in Pakistan and routinely attacks security targets.

Earlier Saturday, officials in northwest Pakistan said 15 militants have been killed in a clash between rival militant Islamist groups.

Authorities say several people were wounded in the battle in the Orakzai tribal region near the Afghan border. It was not immediately clear what caused the clash.

Meanwhile in the south, officials said a bomb partially exploded outside the Red Cross office in Karachi.

Authorities say two motorcyclists delivered the bomb to the site. Officials say there were no injuries from the small blast.