Egypt’s prime minister has apologised for a fresh wave of violence in Cairo last night, which resulted in the death of a further five people as well as several hundred injuries.

PM Ahmed Shafiq described the outbreak as a “fatal error” as anti government protestors clashed with Mubarak supporters in Tahrir Square, which has been the main focus of the protests.

Gunfire lasted for two hours as the demonstrators continued to demand that President Hosni Mubarak, who has ruled for 30 years, step down immediately.

Pro-government supporters retaliated by throwing petrol bombs, wielding sticks and charging on camels and horses.

The Muslim Brotherhood, a formally banned mass movement, issued a statement on Al Jazeera calling for him to be replaced by a national unity government. The Islamist group, whose potential rise to power troubles Mubarak’s Western allies, has so far taken a backseat in the protest movement.

It said: “We demand that this regime is overthrown and we demand the formation of a national unity government for all the factions.”

Egypt’s Health Minister Ahmed Samih Farid said earlier that five people had died in the fighting, which began on Wednesday, and 836 were injured - mostly as the result of stone throwing and attacks with metal rods and sticks.

“This is a fatal error,” Mr Shafiq told Egypt’s al-Hayat television. “When investigations reveal who is behind this crime and who allowed it to happen, I promise they will be held accountable and will be punished for what they did.”

“There is no excuse whatsoever to attack peaceful protesters, and that is why I am apologising,” he said, urging the protesters “to go home to help end this crisis”.

Mr Mubarak has said that he will serve out his current presidential term, which ends in September, but will not run for re-election.

On Wednesday, groups fought pitched battles in Cairo, in the worst violence in 10 days of protests.

The unrest has left about 300 people dead across the country, according to UN estimates.

Clashes were also reported in Egypt’s second city, Alexandria.

US Secretary of State Hillary Clinton told Egyptian Vice-President Omar Suleiman in a phone call on Wednesday that the clashes were a “shocking development” after days of peaceful protests.

She also “underscored the important role that the Egyptian armed forces have played in exercising restraint in the face of peaceful demonstrations”, the state department said in a statement.

Some 350 people working for the UN in Egypt are being evacuated to Cyprus because of the heightened security concerns, according to Rolando Gomez, spokesman for the UN peacekeeping mission.

With many protestors are blaming the government and secret services for cracking down on the previously largely peaceful demonstrations, the United States has renewed its appeal to Mubarak to take steps towards democratic elections at once.

A senior U.S. official also said on Wednesday it was clear that “somebody loyal to Mubarak has unleashed these guys to try to intimidate the protesters”.

The US supplies the Egyptian military with about $1.3 billion in aid. However it has limited powers to force Egyptian authorities to end the violence and begin a transfer of power.

Egypt, which signed a peace treaty with Israel in 1979, justified the emergency rule which kept Mubarak in power as needed to curb Islamist militants and Washington is looking for a way forward which does not encourage even greater instability.

Following Mubarak’s announced on Tuesday that he would step down in September, President Barack Obama telephoned him and said that change “must begin now”.

A Egyptian Foreign Ministry statement on Wednesday rejected U.S. and European calls for the transition to start immediately, saying they aimed to “incite the internal situation” in Egypt.

Oil prices have climbed on fears the unrest could spread to other Arab states including Saudi Arabia or interfere with oil supplies from the Red Sea to the Mediterranean through the Suez Canal.

On Thursday, thousands of anti-government protesters gathered in the Yemeni capital Sanaa demanding a change in government and saying President Ali Abdullah Saleh’s offer on Wednesday to step down in 2013 was not enough.

Along with the United States, France, Germany and Britain have also urged a speedy transition.

But others feared he could either cling on to power, or hand over to a military ruler without allowing truly free and fair democratic elections.