A suspected female suicide bomber killed at least 42 people in a crowd receiving food at a distribution centre in Pakistan's tribal region on Saturday, government officials said.
Seventy others were injured in the attack at Khar, the main town in Bajaur tribal district, where government forces are fighting Taliban and Al Qaeda militants.
Local government official Imtiaz Khan said about 300 people were gathered to receive food when the bomber struck. "According to initial reports, the bomber was a woman wearing a burqa."
"Forty-two people have been confirmed dead while more than 70 people are injured. Seven to eight people are in critical condition," Afif Khan, a medical officer at emergency department in Khar's main hospital, said over the phone.
A witness named Wasi Ullah said a burqa-clad female of 22 to 23 years first hurled hand grenades when stopped at the gate by the security personnel where she detonated her explosives.
"Her body parts including hands and feet were seen lying near the gate," he said.
It was only third known suicide attack in Pakistan by a woman.
Thousands of families displaced by fighting between the military and Taliban fighters rely heavily on food provided by the government and the UN World Food Programme.
Bajaur, one of the insurgents' key launching pads for cross-border raids in Afghanistan, was the scene of a 2006 drone attack at a religious school in Damadola that killed over 80 people.
Officials said Ayman al-Zawahiri, one of top Al Qaeda leaders, was the main target of that strike but he had left the place shortly before the attack.
The military announced last year that the area had been cleared of militants, but it is believed that the insurgents are hiding in the mountainous border regions, and target the army and people in Bajaur and neighbouring Mohmand district.
The bombing came a day after 150 Taliban fighters carried out coordinated attacks on five security posts in Mohmand in which 11 soldiers and 24 militants died, officials said.