Supporters of Egypt's deposed President Mohamed Morsi have urged fresh rallies, raising fears of renewed violence amid warnings from the interim government that police will disperse them soon.

Sit-ins were expected to continue on Friday, extending weeks-long rallies, two days after the interim government authorised police to clear demonstrations "gradually".

"About 33 pro-Morsi marches are due to start after the midday prayer," said Al Jazeera's Hoda Abdel-Hamid, in Cairo.

"They will head to rallies at either Nassr City or near Cairo University. This is the third mass march called for so far this week."

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Al Jazeera's Rawya Rageh, also in the capital, said: "Over the past 48 hours the interior ministry has been clarifying that any approach towards sit-ins is going to be gradual and preceded by several warnings," .

"Up until now, it does not appear that a crackdown is particularly immiment given that were not seeing a security build up around the sit-ins."

No specific date has been announced for the police intervention.

Those camped out at pro-Morsi rallies are using barricades or sand bags to fortify their rallies in the event of further violence, which has so far seen more than 250 people killed in one month.

"Given the record of the Egyptian security forces to break up sit-ins... the move almost always end up in fatalities," our corresepondent said.

Defiant protesters

In an interview with Al Jazeera, Waleed al Haddad, a senior member of the Freedom and Justice Party which represents Egypt's Muslim Brotherhood, pledged to remain on the streets until Morsi was restored to power.

"The people will not leave the squares all over Egypt. We are here for the restoration of legitimacy. ... We are offering our blood, our money, everything in order to restore [democracy]," he said.

"These people will not leave these places. They have only one opportunity to make the people leave  - to kill all the millions here."

In its statements this week, the interior ministry asked those in Rabaa al-Adawiya and Nahda squares "to let reason and the national interest prevail, and to quickly leave"."

On Thursday it pledged "a safe exit and full protection to whomever responds to this appeal," which was subsequently rejected by protesters.

Alpha Oumar Konare: Morsi is in good health

Witnesses on Thursday told Al Jazeera that military helicopters were hovering at low altitude over the sit-in at Cairo’s Rabaa al-Adawiya district, which has been running since Morsi's removal by the military on July 3.

Foreign officials have also stepped up efforts to pressure a way forward.

At the start of the week, Catherine AshtonEU foreign policy chief, and Alpha Oumar Konare, African Union envoy,met Morsi, who remains in jail, reporting that he is in "good health".

Later, two US Republican senators accepted an invite from President Obama to visit Egypt and press for fresh elections.

And on Thursday, Germany's Guido Westerwelle, the first foreign minister to visit Egypt since Morsi was deposed, urged authorities to avoid "the appearance of selective justice".

Most recently, John Kerry, US secretary of state, speaking during a trip to Pakistan, said: "The military was asked to intervene by millions and millions of people, all of whom were afraid of a descendance into chaos, into violence."

Following Ashton's visit to Cairo, he had phoned her to back a call for an "inclusive political process".

Source: Al Jazeera and agencies