PESHAWAR, Pakistan — A car bomb tore through a busy market in northwestern Pakistan today, killing 91 people as U.S. Secretary of State Hillary Rodham Clinton visited the country and pledged American support for its campaign against Islamist militants.

More than 200 people were wounded in the blast in the main northwestern city of Peshawar, the deadliest in a surge of attacks this month. The government blamed militants seeking to avenge an army offensive launched this month against al-Qaida and Taliban in their stronghold close to the Afghan border.

The bomb destroyed much of a market selling bangles, dresses and toys that was popular with women and children.

It collapsed buildings, including a mosque, and set shops on fire in an old part of the city crisscrossed with narrow alleys clogged with stalls.

Crying for help, men grabbed at the wreckage, trying to pull out survivors trapped beneath. One two-story building collapsed as firefighters doused it with water, triggering more panic.

Clinton, on her first visit to Pakistan as secretary of state, was in the capital, Islamabad, when the blast took place. She praised the army's anti-Taliban offensive in South Waziristan and offered U.S. support.

"These extremists are committed to destroying what is dear to us as much as they are committed to destroying that which is dear to you and to all people. So this is our struggle as well," Clinton said.

Appearing with her, Pakistani Foreign Minister Shah Mahmood Qureshi said the violence would not break his government's will to fight back.

"The resolve and determination will not be shaken," Qureshi said. "People are carrying out such heinous crimes — they want to shake our resolve. I want to address them: We will not buckle. We will fight you. We will fight you because we want peace and stability in Pakistan."

No group claimed responsibility, but that is not unusual, especially when the victims are Pakistani civilians. Sahib Gul, a doctor at a nearby hospital, said 91 people were killed and more than 200 injured. Many of the victims were women and children.