CAIRO (AFP) – Secretary of State Hillary Clinton took what she called a "thrilling" tour of Cairo's Tahrir Square, centre of the protests that ousted Hosni Mubarak, on Wednesday, ignoring criticism of Washington's long support for his regime.

The most senior US official to visit Egypt since the veteran strongman's resignation last month, Clinton wandered round the huge central plaza in the morning rush hour accompanied by embassy officials, before heading into talks with Prime Minister Essam Sharaf.

But her tour was overshadowed by a snub from one of the main youth groups that spearheaded the Tahrir demonstrations and by a deadly police raid on a protest camp in US Gulf ally Bahrain which killed three demonstrators and wounded dozens more.

"To see where this revolution happened and all that it has meant to the world is extraordinary for me," Clinton said as she toured the square protected by Egyptian and US security guards.

"It's just a great reminder of the power of the human spirit and universal desire for freedom and human rights and democracy," she added.

"It's just thrilling to see where this happened."

Clinton was greeted by a dozen or so ordinary Egyptians in the square but others further away in the morning crowds were seen to frown as she passed.

"Thank you for walking the streets of Tahrir," one man told her.

Another held his young daughter aloft, prompting her as she said in English: "I love you." Clinton clasped her hand.

As she posed for the cameras alongside the Egyptian premier before their talks, the US chief diplomat again waxed lyrical about her tour of the square and promised Washington's full support.

But outside the prime minister's office, dozens of workers of the Petrojet oil firm were demonstrating to get their full-time jobs back.

"It was very exciting and moving for me to go to Tahrir Square and to have some sense of what those amazing days must have been like here in Cairo," she said.

"I am so looking forward to helping in anything that we can in this transformation and all the work that needs to be done.

"There is so much to be done and the US stands ready to help in everything possible to translate what happened in Tahrir Square into (a) new reality for Egypt."

But Washington's swift and apparently unapologetic switch from staunch Mubarak ally to supporter of the transition failed to convince the ringleaders of the Tahrir protests.

The Coalition of the Youth of the Revolution said it had snubbed an invitation to meet Clinton because of "the US administration's weak position at the start of the revolution due to its close relationship with the ousted president."

The group added that it had also been angered by "the help and support offered by the American administration to many of the oppressive and undemocratic regimes in the region," in a statement posted on its website on Monday.

The United States bases its Fifth Fleet in Bahrain, where deadly violence raged on Wednesday as security forces assaulted a protest camp in the capital Manama's Pearl Square modelled on the Tahrir demonstrations after the authorities declared a state of emergency.

Nationwide protests calling for Mubarak to step down and demanding political and economic change erupted on January 25.

The rallies, which saw bloody clashes between protesters and security forces, left at least 384 people dead and more than 6,000 injured.

After a series of concessions failed to placate the protesters, Mubarak resigned on February 11 and handed power to a military council, which has vowed to pave the way for a swift return to civilian rule and a democratic system.