Clashes erupted Tuesday between student supporters of Egypt's ousted Islamist president Mohammed Morsi and security forces in several cities, wounding at least 33 people, the health ministry said.

The violence came as registration of candidates for the May 26-27 presidential election entered its second day, with former army chief Abdel Fattah al-Sisi, who led Morsi's ouster last July, widely expected to win.

British Prime Minister David Cameron said Tuesday he had ordered an investigation into the Muslim Brotherhood over concerns that the group, declared a terrorist organization by Egypt and Saudi Arabia, is linked to violent extremism.

Key leaders of the group have been based in London since the toppling of the Islamist Egyptian president Mohammed Morsi last year and a crackdown that has seen hundreds killed and thousands arrested.

The father of Al-Jazeera journalist Peter Greste said Tuesday that the Australian's trial in Egypt over alleged links to the banned Muslim Brotherhood was "psychological torture" for his family.

Greste has denied charges of spreading false news and supporting the blacklisted Muslim Brotherhood movement of deposed Islamist president Mohamed Morsi but was refused bail on Monday after appearing in court in a caged dock.

An Egypt court on Monday sentenced 33 supporters of ousted president Mohamed Morsi to six-year jail terms each for committing acts of violence during an unauthorized protest, judicial sources said.

The accused, deemed by the court to be members of Morsi's Muslim Brotherhood, were found guilty of violent acts during clashes between Islamist demonstrators and opponents of Morsi in the Mediterranean city of Alexandria last December, the sources said.

An Egyptian court on Monday rejected a plea for bail by jailed Al-Jazeera journalists, who denied links with the blacklisted Muslim Brotherhood in a trial that has sparked international condemnation.

The journalists, who have spent nearly 100 days in jail since their arrest, are charged with spreading false news and supporting the Islamist movement of deposed president Mohammed Morsi.

An Egyptian minister on Sunday accused an editor of Al-Jazeera television of helping leak classified intelligence documents in an espionage case involving deposed president Mohammed Morsi.

The accusation came a day before a trial of three journalists with the Doha-based broadcaster resumes in Cairo on charges of spreading false news and supporting Morsi's Muslim Brotherhood.

Egypt is to hold a presidential election on May 26-27, 10 months after the army ousted Islamist leader Mohammed Morsi from the presidency, the electoral commission announced on Sunday.

Retired army chief Abdel Fattah al-Sisi, who toppled Morsi, is widely expected to win the vote, riding on a wave of popularity for having removed the divisive president last July.

An Egyptian court on Saturday sentenced to death two supporters of deposed president Mohammed Morsi convicted of throwing youths off an apartment block roof, judicial sources said.

One youth thrown from the building in Alexandria was killed. The court submitted its verdict for approval to the mufti, the government's official interpreter of Islamic law, the sources said.

The Gaza Strip's land border with Egypt reopened Saturday after a 50-day closure, but only for three days and then just for special cases, its Islamist rulers Hamas said.

Passage to Egypt will be limited to those seeking medical treatment, students going to their places of study, foreigners and in cases deemed as humanitarian, Hamas's interior ministry said.

Five people including an Egyptian woman journalist were killed in Cairo Friday as police clashed with Islamists protesting against ex-army chief Abdel Fattah al-Sisi's presidency bid, the interior ministry said.

The violence erupted in a deeply polarized Egypt as supporters of deposed president Mohammed Morsi took to the streets of Cairo, Alexandria and other cities to vent their anger at Sisi who overthrew the Islamist leader nine months ago.