Tens of thousands of people in a mass rally i
Tens of thousands of people in a mass rally iAFP photo

Tens of thousands of people packed Cairo’s Tahrir Square on Tuesday, to protest a power grab by President Mohammed Morsi, piling pressure on him as he faces his most divisive crisis since taking power in June.

AFP reported that the huge turnout in the iconic square in the heart of Cairo, as well as in the Mediterranean city of Alexandria and most of Egypt's 27 provinces, marked the largest mobilization yet against the president.

Elsewhere in the country, protesters enraged by Morsi's decision to grant himself sweeping powers attacked three regional headquarters belonging to the president's Muslim Brotherhood movement, a security official told AFP.

In Tahrir, protesters who had voted for Morsi in the election joined forces with die-hard opponents of the Islamist.

"I'm here to protest Morsi's autocratic decisions," Mohammed Rashwan, an engineering graduate who voted for Morsi, told AFP.

"I have discovered that he is pro-Muslim Brotherhood and not the revolution," Rashwan added.

Throughout the afternoon and into the evening on Tuesday, marches poured into Tahrir Square, swelling the numbers, amid an electrifying atmosphere many said reminded them of the 2011 uprising which led to the ouster of former President Hosni Mubarak.

The protesters are angry at the decree that Morsi announced last Thursday allowing him to "issue any decision or law that is final and not subject to appeal", which effectively placed him beyond judicial oversight.

The decree put him on a collision course with the judiciary and consolidated the long-divided opposition which accuses him of taking on dictatorial powers.

The demonstrations were held a day after Morsi stuck by his decree after a meeting with the country's top judges aimed at defusing the crisis.

"The solution is to cancel the constitutional declaration... We won't replace a dictator with another," said protester Asser Ayub, 23, waving an Egyptian flag.

In the Mediterranean city of Alexandria, thousands gathered in Qait Ibrahim square, reported AFP. The Muslim Brotherhood wrote on its Twitter account that it ordered its members to evacuate the group's headquarters after it came under attack.

Protesters also stormed and ransacked the group's headquarters in the Nile Delta city of Mansura, a security official said, and attacked the group’s office in the city of Mahalla.

Three people have died in clashes since Morsi decreed his new powers on Thursday, reported AFP. A rival rally in Cairo by the Muslim Brotherhood in support of the president was called off to "avoid potential unrest" but that has done little to abate the split between Morsi's supporters and foes.

Republican U.S. Senator John McCain warned on Sunday that Egypt could become an Islamist state or face another military takeover if Morsi's judicial power grab is left unchecked.

McCain, the 2008 Republican presidential nominee, urged President Barack Obama to be prepared to use billions of dollars of American aid as leverage to force Morsi to change course.