President Barack Obama is strongly condemning what he calls the "outrageous" terrorist attack in Pakistan that killed at least 45 people.

Authorities say a burqa-clad female suicide bomber in Pakistan lobbed hand grenades, then detonated her explosive belt among a crowd at an aid center Saturday, killing at least 45 people in militants’ latest strike against the authorities’ control over the key tribal region bordering Afghanistan.

In a statement released in Honolulu, Hawaii, where he was spending Christmas, Obama said, "Killing innocent civilians outside a World Food Program distribution point is an affront to the people of Pakistan, and to all humanity."

Police believed it was the first time Islamic militants have sent a woman to carry out a suicide attack in Pakistan, where the U.S.-led war in Afghanistan against al-Qaida and the Taliban insurgents continues to spill over despite Islamabad’s repeated claims of victory on its side of the porous border.

The bomber, dressed in the head-to-toe burqa robes that women commonly wear Pakistan and Afghanistan, was challenged by police at a check point, officials said.

She then charged toward a group of 300 people lined up outside the food aid distribution center in the town of Khar, tossing two hand grenades before blowing herself up, officials said. The crowd was made up of people who have fled conflicts elsewhere in the area.

The attack in Khar, the main city in the Bajur region of Pakistan’s northwest, came a day after 150 militants waged pitched gun battles against five security posts in the adjourning Mohmand tribal region to the south. The fighting, which left 11 soldiers and 24 militants dead, was an unusually strong show of strength by insurgents in border country that the military has twice claimed to have cleaned of militants.

Helicopter gunships backed by artillery continued the battle on Saturday, pounding enemy hideouts and killing another 40 militants, said Amjad Ali Khan, the top government official in Mohmand.

The tribal regions are of major concern to the U.S. because they have been safe havens for militants fighting NATO and American troops across the border in Afghanistan. The U.S. has long pressured Pakistan to clear the tribal belt of the insurgents.

The Pakistani Taliban claimed responsibility for Saturday’s suicide attack in Khar, through its spokesman, Azam Tariq.