Thousands of police and soldiers were deployed across the Egyptian capital Monday ahead of planned demonstrations against the government's transfer of two islands to Saudi Arabia.
The has already sparked the biggest protests since President Abdel-Fattah el-Sissi assumed power nearly two years ago.
Riot police backed by armored vehicles took up positions in Cairo's Tahrir Square, the epicenter of Egypt's 2011 uprising, as well as other sites including a suburban square where at least 600 Muslim Brotherhood supporters were killed by security forces in August 2013.
The military said in a video released late Sunday that troops were deployed to protect "vital and important installations" and deal with anyone who tries to "harm the people's interests or attempt to ruin their happiness" on Monday, which was also Sinai Liberation Day — a national holiday marking the completion of Israel's withdrawal from the peninsula in 1982.
Egyptian warplanes roared over Cairo to mark the anniversary, but the military kept a low profile on the ground except for in the Cairo suburb of Heliopolis, home to military headquarters and the presidential palace. The Interior Ministry said police were out in force to protect "peaceful" citizens who wish to celebrate.
El-Sissi has urged citizens to defend the state and its institutions from the "forces of evil," an apparent reference to the planned protests.
Monday's demonstrations would be the second wave of protests this month against the decision to give up control of two islands at the mouth of the Gulf of Aqaba. On April 15, about 2,000 demonstrators protested in downtown Cairo over the islands.
That protest was the largest against el-Sissi since he assumed office in 2014, nearly a year after leading the military ouster of the Islamist Mohammed Morsi, Egypt's first freely elected leader.
Authorities have detained dozens of activists in recent days, with the arrests continuing until just hours before the planned demonstrations. Freedom for the Brave, an activist group, says nearly 100 people have been arrested since the latest round of detentions began last week.
Egypt says the islands of Tiran and Sanafir, off the southern coast of the Sinai Peninsula, belong to Saudi Arabia, which placed them under Cairo's protection in 1950 because it feared Israel might attack them. The government says officials and experts have for years negotiated with their Saudi counterparts and agreed that the islands are inside Saudi Arabia's territorial waters.
The announcement came during a visit to Egypt this month by the Saudi monarch, King Salman, as the kingdom announced a multi-billion-dollar package of aid and investment to Egypt, fueling charges that the islands were sold off.
El-Sissi insists that Egypt has not surrendered an "inch" of its territory and has demanded that people stop talking about the issue.