Egyptians are braced for possible bloodshed ahead of mass rallies in support of both sides of the country's deep political divide. This comes three weeks after the military removed the country's elected president.
Supporters of former Islamist President Mohammed Morsi and the army, which ousted him on July 3, are expected to turn out in large numbers for rival rallies on Friday.
This follows an unusual move by the head of the country's military, General Abdel-Fattah el-Sissi, who earlier this week urged the Egyptian people to take to the streets in mass demonstrations this Friday. El-Sissi said this was needed to give the military a "mandate" to take any measures it deems necessary to quell "violence and terrorism."
Many, including members of Morsi's Muslim Brotherhood, fear these words were a veiled threat to crack down on the supporters of the movement, who have been staging sit-ins in the capital, Cairo, and other cities to demand that the ousted president be returned to power.
A military statement issued late on Thursday did nothing to allay such fears.
"The general commander of the armed forces has given a 48-hour deadline for a backdown and to join the national ranks," an army statement cited by Egypt's state-run Middle East News Agency said. "The armed forces and police will not allow any infringement of national security whatever sacrifices are," it added.
However, there was no immediate sign that Morsi's supporters had any plans to comply with this demand.
They had already responded to el-Sissi's call for mass demonstrations on Friday, by organizing protests of their own.
Earlier on Thursday, Muslim Brotherhood leader Mohammed Badie appealed to the religious sentiments of supporters in an effort to get them to turn out in high numbers on Friday to protest against "the bloody military coup."
"I swear by God that what el-Sissi did in Egypt exceeds the enormity of his clutching an axe and destroying the holy Kaaba one stone after the other," Badie in a statement posted on the Brotherhood's website and referring to the Muslim holy site in Mecca.
Badie has not been seen in public for more than two weeks, since the authorities ordered him arrested on charges of inciting violence. He is belived to be hiding in a Cairo mosque.
Dozens of people have been killed in clashes since the army removed the democratically elected Morsi from power amid mass demonstrations against him.
Concerns in the West
Developments in Egypt have caused growing concerns in the West. The United States signalled its displeasure earlier in the week, by announcing that it would delay the planned delivery of four F-16 fighter jets to the Egyptian military.
On Thursday though, Washington also decided not to declare the military takeover as a coup, something which would have forced it to cut off aid to Egypt, according to an unnamed senior US official quoted by the Reuters news agency.
Also on Thursday, United Nations Secretary-General Ban Ki-moon called for Morsi and other arrested senior Brotherhood members to "be released or have their cases reviewed transparently without delay."
Speaking to reporters in New York, UN deputy spokesman Eduardo del Buey said the secretary-general had also called on all sides to "act with maximum restraint."
pfd/ch (AP, Reuters, dpa)