The United Nations said Friday that international help is needed to feed 1.5 million people in crisis-torn Syria, but humanitarian corridors were not yet justified.

U.N. humanitarian chief Valerie Amos said almost three million people out of Syria's population of about 20.5 million had been affected by the deadly crackdown on protests launched by President Bashar Assad since March.

Protesters blocked the entrance to Egypt's cabinet headquarters on Friday in a bid to prevent newly-named Prime Minister Kamal al-Ganzuri from entering the building, an AFP reporter said.

The action was in protest at Ganzuri's appointment, one of the organizers, Ahmed Zahran, told AFP, adding that a news conference would follow shortly.

Syrian security forces on Friday pressed a months-long crackdown on dissent, killing six more people with gunfire as protesters flooded streets in support of a rebel army, activists said.

The latest violence came as an Arab League 1100 GMT deadline for Syria to accept an observers' mission or face sanctions passed with no response from Damascus.

The U.N. Committee Against Torture said on Friday it had received reports of massive human rights violations in Syria, including the detention and mutilation of children.

"The committee has reviewed numerous, consistent and substantiated reports and information about widespread rights violations in the country," the head of the panel Claudio Grossman said in a statement.

The imam leading tens of thousands of worshippers in prayer at Cairo's Tahrir Square on Friday called on the ruling military to hand power to a national salvation government.

Sheikh Mazhar Shahin said protesters would remain in the square -- the symbolic heart of rallies that toppled President Hosni Mubarak -- until their demands were met.

Fierce clashes broke out between rival security forces in the Yemeni capital Friday, two days after President Ali Abdullah Saleh inked a power transfer deal which sponsors had hoped would end the violence.

Dissident troops from the First Armored Brigade led by General Ali Mohsen al-Ahmar exchanged mortar and machinegun fire in the early hours with forces of the central security services commanded by Saleh's nephew Yehya, residents said.

Thousands of supporters of Egypt's ruling military council turned up for a rally in Cairo's Abassiya neighborhood on Friday, just miles from a mass protest in Tahrir Square calling for the end of military rule.

"The military, the police and the people are one," the protesters chanted according to the MENA news agency.

Syrian activists called for demonstrators to flood the streets nationwide after the main weekly Muslim prayers in support of dissident army officers.

"The free army protects us," said a message on the Facebook page of the Syrian Revolution 2011, one of the key motors behind more than eight months of protests seeking to unseat the government of President Bashar Assad.

Russia said Friday ahead of the expiry of a new Arab League ultimatum on Syria that it opposed pressure and sanctions against its traditional Arab ally and wanted to see a renewal of political dialogue.

"At this stage, what we need is not resolutions, sanctions or pressure, but inter-Syrian dialogue," foreign ministry spokesman Alexander Lukashevich told a televised press briefing.

A new Arab League ultimatum which gives Syria until later Friday to agree to accept observers or face sanctions represents a last chance for the regime in Damascus, Turkey's foreign minister said.

"It is a last chance, a new chance for Syria," Ahmet Davutoglu told reporters in Istanbul in the final hours before the 11:00 GMT deadline.