Several protests were held Friday in Cairo and other parts of Egypt denouncing a government plan to cede strategic islands to Saudi Arabia, witnesses and local media said.
Police used tear gas to break up anti-government rallies in at least three areas in the city of Giza near Cairo, according to reports and witness accounts.
There were also reports of arrests in Giza, but further details were not available.
Twenty-five demonstrators were arrested in Alexandria, Egypt’s second-biggest city, state-run newspaper al-Ahram reported, citing an unnamed security official.
The Egyptian government said this week that technical work on demarcating a maritime boundary with Saudi Arabia had revealed that the Red Sea islands of Tiran and Sanafir lay within Saudi territorial waters.
The announcement, made as Saudi Arabia's King Salman was on a visit to Cairo, triggered a public outcry and sharp criticism from the opposition.
Hundreds of protesters gathered outside the Journalists’ Syndicate in central Cairo Friday, where anti-riot police were heavily deployed to prevent demonstrators from marching to the nearby iconic Tahrir Square.
Tahrir was the epicentre of the 2011 uprising, which forced longtime president Hosny Mubarak out of power.
Some demonstrators on Friday chanted slogans against an agreement related to the two islands, saying: “They’ve sold the land to Saudis,” and “The sale is invalid.”
Other protesters singled out President Abdel-Fatah al-Sissi with their anger. "Go!" they shouted, echoing a popular slogan during the anti-Mubarak revolt.
The protests were the first in months in Egypt, where street demonstrations are banned without prior permission from police.
They came in response to an online call by secular activists and the now-banned Muslim Brotherhood to hold mass protests dubbed “land is honour.”
Tiran and Sanafir control the southern entry to the Gulf of Aqaba, where both Israel and Jordan maintain important ports.
Egyptian parliament must ratify the accord before it becomes effective. Al-Sissi's backers dominate the legislature.
Critics have alleged that the island surrender is in return for economic aid from Riyadh, a claim that al-Sissi has denied.
Saudi Arabia has given significant financial and diplomatic backing to Egypt since 2013, when al-Sissi, the then army chief, deposed president Mohammed Morsi of the Muslim Brotherhood.
Al-Sissi took office in 2014 following an election landslide.
In recent months, he has come under increasing criticism at home over alleged massive rights abuses and economic woes.