Security forces have arrested an Egyptian on suspicion of spying for Israel, Egypt's state prosecutor said on Saturday, adding that it has detained him for 15 days for questioning.

Official news agency MENA, which carried the prosecutor's comments, added that the man is accused of having worked for Mossad, Israel's foreign intelligence service.

Thousands of Islamists rallied in the Egyptian capital on Friday in support of calls by Sunni Muslim clerics for a holy war against the regime of Syrian President Bashar Assad.

The demonstration took place outside a Cairo mosque where Saudi preacher Mohammed al-Oreifi called in a sermon for a "jihad in the cause of Allah in Syria."

Ethiopia's parliament ratified a controversial treaty Thursday ensuring its access to Nile water resources, amid bitter arguments with Egypt triggered by an Ethiopian dam project.

The deal replaces a colonial-era agreement that granted Egypt and Sudan the majority of water rights and allows upstream countries to implement irrigation and hydropower projects without first seeking Egypt's approval.

Ousted president Hosni Mubarak, his wife and one of their sons are to return gifts worth a total of $600,000 (450,000 euros) to Egypt's former information minister, a judicial source said on Wednesday.

The source, quoted by state news agency MENA, said the prosecutor's office accepted a proposal from the Mubaraks to return the gifts and Gamal Mubarak had signed the necessary paperwork.

Egyptian Islamist parties, including the president's, on Wednesday called for a "million-man march" on June 21 to counter a planned protest at the end of the month outside the presidential palace.

"Islamist parties have decided to organize a 'million-man march' in front of Rabaa al-Adawiya mosque (in a Cairo suburb) on Friday, June 21, under the slogan: 'Protect the revolution. Yes to peace, no to violence'," said President Mohamed Morsi's Freedom and Justice Party, political arm of the Muslim Brotherhood, on its website.

Supporters and opponents of Egypt's Islamist President Mohamed Morsi clashed on Tuesday outside the culture ministry, where artists have been protesting against what they see as efforts to impose a religious agenda.

Dozens of Islamist protesters and anti-government demonstrators fought outside the ministry headquarters in the Cairo neighborhood of Zamalek leaving several lightly injured, Agence France Presse reporters said.

Egyptian President Mohammed Morsi has warned that "all options are open" in confronting an Ethiopian project to build a dam on the Blue Nile, which may diminish Egypt's water supply.

"I confirm that all options are open to deal with this subject," the Islamist president told hundreds of his supporters late Monday at a conference on the issue.

Egypt's foreign minister is to hold talks in Addis Ababa on Ethiopia's plan to build a Nile dam that has stirred "life or death" concerns over water resources, the premier announced Monday.

Hisham Qandil told the Senate, taking the place of parliament until a new National Assembly is elected, that Foreign Minister Mohammed Kamel Amr would travel to Ethiopia "in the coming days to give the Egyptian point of view" on the project.

Toppled president Hosni Mubarak's retrial was adjourned until July on Monday after new documents and videos were submitted over his alleged complicity in the killings of protesters during Egypt's 2001 revolution.

The criminal court in Cairo, on a technicality, also ordered the release of his two sons, Alaa and Gamal Mubarak, who have been on trial along with the former leader on corruption charges.

Tens of the supporters of the Muslim Revolutionaries movement in Egypt on Sunday staged a sit-in in front of the Lebanese embassy in Cairo to protest Hizbullah's involvement in the Syrian war.

The Egyptian daily al-Shourouq reported that the protesters chanted slogans denouncing the party as the security forces brought reinforcements to the neighborhood where the embassy in located.