At least 91 people have been killed after a car bomb ripped through a busy market in Peshawar, Pakistan.

The attack, which injured scores more people, was the deadliest to hit Pakistan this year.

Similar attacks have killed more than 200 people in recent weeks, as the army carries out an operation against Taliban militants in South Waziristan.

The blast came as US Secretary of State Hillary Clinton began a visit to the Pakistani capital, Islamabad.

Mrs Clinton told a news conference the US was "standing shoulder to shoulder" with Pakistan in its fight against "brutal extremist groups".

Local officials blamed the Taliban for Wednesday's car bombing, though no claim of responsibility was reported.

The blast tore through buildings in Peshawar's Peepal Mandi market street, setting several of them on fire.

The market mostly sells products for women, and women and children were among the dead.

"There was a huge blast. There was smoke and dust everywhere. I saw people dying and screaming on the road," eyewitness Mohammad Siddique told the AFP news agency.

Crowds dug through rubble to rescue people.

'No security'

Sahib Gul, a doctor at a nearby hospital, told AP that 91 that people had been killed and more than 200 injured. Medical staff appealed for people in Peshawar to give blood.

Some complained that the authorities were not prepared to deal with the aftermath of such a large attack.

"There are a lot of wounded people. We tried to help them but there were no ambulances so we took the victims on rickshaws and other vehicles," Muzamil Hussain told the Associated Press.

"There were no police. The police and government didn't help us, the police even opened fire on us."

Another man said dead and injured people were still trapped in fallen buildings.

"We are afraid that they will die. There is no security. We have been fooled in the name of security," he said.

Security has been stepped up across Pakistan, but the government still appears to be unable to stop the attacks, says the BBC's Mark Dummett in Islamabad says.

Foreign Minister Shah Mahmoud Qureshi promised that the country's resolve would not be shaken by "such heinous crimes".

In a press conference in Islamabad with Mrs Clinton, he told potential militants: "We will not buckle, we will fight you. We will fight you because we want stability and peace in Pakistan."

'Brutal extremists'

Mrs Clinton is in Pakistan to discuss US concerns about the increasing numbers of militant attacks and the security of the country's nuclear weapons.

Speaking in Islamabad, she condemned the "vicious and brutal" attack in Peshawar and said the fight against the Taliban was "not Pakistan's alone".

"Pakistan is in the midst of an ongoing struggle against tenacious and brutal extremist groups who kill innocent people and terrorise communities," she said.

"We commit to stand shoulder to shoulder with the Pakistani people in your fight for peace and security, we will give you the help that you need in order to achieve your goal.

Last week, Pakistan launched an offensive in South Waziristan, which is considered to be the main sanctuary for Islamic militants outside Afghanistan.

Correspondents say the Peshawar blasts will come as a violent reminder for the US of the difficult task it is facing in the fight against the Taliban, both in Pakistan and across the border in Afghanistan.