Egypt's police have "encircled" major routes into Cairo as the government attempts to prevent a planned protest over the decision to hand two Red Sea islands to Saudi Arabia.
The Interior Ministry increased security around the capital on Friday to prevent what it called "infiltration of the terrorist group" - a reference to the banned Muslim Brotherhood.
Though the authorities have accused the Brotherhood of organizing "tendentious" protests, a variety of groups have called for protests.
The ministry on Thursday night put out a statement urging Egyptians "not to get carried away by tendentious calls for protests" and warning against any attempts to break the law.
The statement added that the ministry will take "all decisive legal measures" to maintain security.
Despite the strict security measures, protest marches set out from 30 mosques across the country after Friday prayers.
Protesters vented their anger at President Abdel Fattah el-Sisi's decision to give Saudi Arabia control of Red Sea islands of Tiran and Sanafir, reports from Cairo said.
“Our right to this land is won by blood, not by documents and maps,” organizers wrote on Facebook page of the event.
“We gave more than 100,000 martyrs in our wars with Israel to restore this land. Tiran and Sanafir are our right, Egypt’s right, the right of our children and of our ancestors who were killed there. This right must be returned, even over our dead bodies,” they added.
Israel briefly occupied Tiran during the Suez Crisis in late 1956, and once more between 1967 and 1982 following the Six Day War.
According to Israeli media, Egypt informed Tel Aviv about its intention to give away the two strategic islands and received the Israeli blessing.
The daily Haaretz said Israel expressed its approval of the give-and-take during talks with the Egyptian side provided that freedom of navigation for Israeli ships through the area were guaranteed.
Israel also demanded that all other commitments undertaken by Egypt under the Camp David peace accord with Tel Aviv be honored, it added.
Foreign Minister Adel al-Jubeir has said Saudi Arabia “will honor all of Egypt’s legal and international commitments in regard to the two islands” in a move seen by Israeli media as an attempt to appease Israel.
Thousands of protesters were anticipated to take part in the mass demonstration, organized by April 6 Youth Movement.
Egypt is reportedly receiving USD 20 billion in aid from Saudi Arabia in return for the move.
Thousands of Egyptians have taken to social media websites over the past few days and accused President Abdel Fattah el-Sisi of surrendering Egyptian territory in return for Saudi money.
Sisi has asked his critics to end discussions about the issue, saying “Egypt did not relinquish even a grain of sand. All the data and documents say nothing except that this particular right is theirs (Saudis).”
Tiran Island is located at the entrance of the Straits of Tiran, which separates the Red Sea from the Gulf of Aqaba. Its strategic significance lies in the fact that it is an important sea passage to the major ports of Aqaba in Jordan and Eilat in Israel.
Sanafir Island is in the east of Tiran Island, and measures 33 square kilometers (13 square miles) in area.
Ownership of the two islands was handed to Egypt in 1982, when Tel Aviv and Cairo signed the so-called Camp David peace accords.