CAIRO — Egypt’s interior ministry said on Thursday it would take legal action against people who participate in demonstrations called by activists to protest Egypt’s unexpected decision to transfer two Red Sea islands to Saudi Arabia.

The ministry urged Egyptians “not to get carried away by tendentious calls for protests and it warns against any attempts to break the law,” adding in a statement that it would take “all decisive legal measures” to maintain security.

Egypt’s media has been in uproar since the government announced on Saturday the signing of a maritime demarcation accord that puts two islands at the southern entrance to the Gulf of Aqaba in Saudi waters.

Saudi and Egyptian officials say Tiran and Sanafir belong to the kingdom and were only under Egyptian control because Saudi Arabia asked Egypt in 1950 to protect them.

On Wednesday President Abdel Fattah al-Sisi tried to calm the furor, reiterating the government’s assertion that the islands had always been Saudi and that Egypt had only been looking after them.

Calls for protest have gathered thousands of supporters on Facebook, including the outlawed Muslim Brotherhood. Eleven people protested against the transfer of the islands earlier this week and five of them were briefly detained.