KHAR, Pakistan – 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.

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.

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.