Tens of thousands of supporters of Egypt's Muslim Brotherhood massed in main squares in several cities on Friday, waving pictures of Mohammed Morsi and chanting that the head of the military is a "traitor," stepping up denunciations of the army over its removal of the country's first freely elected president.

Islamists are trying to escalate their campaign of street rallies aimed at forcing the reinstitution of Morsi. At the same time, the new military-backed administration has intensified its crackdown on the leadership of Morsi's Brotherhood, starting criminal investigations against Morsi and issuing arrest warrants on a host of others.

At the main Islamist rally in Cairo, the crowd poured into a large boulevard in front of a main mosque where Morsi supporters have been camped out for two weeks. During the day, the crowd appeared smaller than in previous days, though it was expected to pick up after sunset and the end of the daily fast of the Islamic holy month of Ramadan.

"We are ready to stay for a month, two months, a year or even two years," an ultraconservative Salafi cleric, Safwat Hegazi, told protesters from a state set up in front of the Rabaa al-Adawiya Mosque. "Some women proposed to bring ovens to bake sweets for the Eid," he said, referring to the festive holiday that marks the end of Ramadan, just under four weeks from now.

During Ramadan, which began Wednesday, Muslims abstain from food and drink from sunrise to sunset, which usually cuts down on activity during the day — particularly outdoors in warm summer temperatures. Some in the square stayed in tents during the day Friday, sleeping or reading the Quran. Islamists also held rallies in the Mediterranean city of Alexandria and several other cities.

Despite the vows to continue until Morsi is back in the palace, the Brotherhood and other Islamists face the question of how to step up their campaign at a time when the new administration is pushing ahead quickly with its transition plans, in part to create a reality and force isolate the Brotherhood by showing the country is moving toward democracy. At the same time, authorities are pulling out multiple allegations aimed at showing Morsi's supporters are linked to violence and militancy.

On Friday, some protesters marched from Rabaa al-Adawiya toward the Republican Guard headquarters, where on Monday troops killed more than 50 Morsi supporters in clashes at an Islamist sit-in. The military says the Islamists sparked the clashes by shooting at troops, though the protesters say the troops attacked them without provocation.

A number of Brotherhood leaders with arrest warrants against them are permanently staying at a medical center connected to the Rabaa al-Adawiya, Brotherhood spokesman Ahmed Aref told The Associated Press, though he underlined that they are not hiding from arrest. Among them are Mohammed el-Beltagy, a leadership figure, and the deputy head of the Brotherhood's political party Essam el-Erian — though Aref said the Brotherhood's spiritual leader, Mohammed Badie, is not at the site. Aref said he did not know where Badie was.

Morsi has been held in an undisclosed military facility since the coup against him on July 3, sparked after four days of massive protests by millions nationwide demanding his removal. Five other Brotherhood leaders are also in detention on various charges, and 10 others — including Badie — have arrest warrants against them on accusations of triggering clashes on Monday. More than 50 of Morsi's supporters were killed in those clashes, outside a headquarters of the Republican Guards.

Gehad Haddad, the group's spokesman, said in a message posted on his Twitter account that those in detention are "denied visitation, or delivery of clothes, food. All held in solitary confinement."

On Friday, Germany Foreign Ministry called for Morsi's release and end to "all restrictive measures considering Morsi" and giving access to an organization such as the International Red Cross to visit the deposed leader.

A day earlier, prosecutors said they will investigate allegations that Morsi and 30 others Brotherhood leaders escaped from prison during the 2011 revolution with help from the Palestinian militant group Hamas.

Anger at the military was rife at Friday's rallies. Protesters carried posters depicting army chief Gen. Abdel-Fattah el-Sissi with blood coming out of his mouth and emblazoned with "traitor." Some banners appeared to be addressing foreign media, with English slogans like, "legitimacy is a red line" — underlining that Morsi is the country's legitimate president.

"This is a coup," said a 20-year-old Ahmed Ismail. "We are going back 100 years to a police state and if we shut up now we won't have any voice in the future," he added.

Mostafa Youssef, 27-year-old-cleric described the military-backed interim President Adly Mansour and his administration as "puppets while the real power is in the hand of the Supreme Council of Armed Forces. Civilians are just a facade."

Protesters in helmets and home-made body shields and sticks, formed human chains guarding the square, with some self-searching visitors.