CAIRO, Apr 24 (Aswat Masriya) - Egyptian prosecutors ordered on Monday the detention of a prominent political activist and member of the April 6 Youth Movement, along with three others, for four days pending investigation.

According to lawyer Doaa Mostafa, who is handling the case, the prosecution accused Sherif al-Roubi, who was arrested on Friday, of belonging to a "terrorist group" and calling for protests planned for Apr. 25.

Several political forces and public figures have called on Egyptians to participate in Monday's protests. These include the Egyptian Social Democratic Party and the Strong Egypt Party, in addition to a number of student groups and youth movements and the two former presidential candidates Hamdeen Sabahi and Khaled Ali.

The April 6 Movement was one of the main actors in the January 2011 Uprising, which resulted in the ouster of former president Hosni Mubarak after he ruled the country for 30 years. 

The movement later split into two groups. Rubi is a member of the "democratic front".

The April 6 democratic front movement and the now-banned Muslim Brotherhood group were among the political forces that called on people to protest on Apr. 25 against the Egyptian-Saudi border agreement.

The protests coincide with Sinai Liberation Day, which is a national holiday across Egypt.

A recently signed border demarcation agreement between Egypt and Saudi Arabia has stirred controversy in Egypt. The agreement stipulates tht Egypt will hand over control over two Red Sea islands to Saudi Arabia.

Critics argue that the two islands are Egyptian and accuse President Abdel Fattah al-Sisi of "selling Egypt" to Saudi Arabia in return for Saudi aid.

Under the slogan "Friday of the Land", thousands of protesters had gathered in front of the press syndicate on Apr. 15 to protest against the agreement, which has yet to be ratified by the parliament.

Protesters ended the demonstration then but said they will resume protesting on Apr. 25.