Kidnappers on Wednesday released three Egyptian policemen and four soldiers seized in the Sinai, the army said, leading to the reopening of a Gaza border crossing that police closed to protest the abductions.

"The seven security personnel have been released by their kidnappers in Sinai," military spokesman Ahmed Aly said in a statement carried by Egypt's official MENA news agency.

Egyptian police arrested 12 members of the "Black Bloc" -- a violent group opposed to the Muslim Brotherhood -- after clashes outside Cairo's presidential palace, the official MENA news agency said on Saturday.

Protesters hurled rocks and fire bombs at the walls of the presidential palace in Heliopolis, and torched a police vehicle, a security source told MENA.

Sectarian violence that erupted overnight north of Cairo killed five people, including four Christians, and left six other people wounded, an Egyptian security source said on Saturday.

The clashes, which saw the use of firearms, flared on Friday night in Al-Khusus, a poor area in Qalyubia governorate, after a Muslim in his 50s objected to children drawing a swastika on a religious institute, the source told Agence France Presse.

Cairo's international airport will be partly closed at night due to fewer incoming flights and to save energy, reports said on Monday, highlighting the economic crisis sweeping Egypt.

Two runways will be closed for four hours starting from 1.30 am (2330 GMT) "in order to save energy", said civil aviation minister Wael al-Maadawi in statements carried by the press.

The headquarters of the Egyptian Football Association were set ablaze on Saturday, minutes after a police officers' club was torched following sentencing over a deadly football riot last year.

Firefighters were working to put out the fire which spread through the building located in the same neighborhood as the officers' club, an Agence France Presse reporter said.

An Egyptian court on Saturday upheld death sentences for 21 defendants over a deadly football riot in Port Said, in a case that has already sparked widespread violence and threats of further unrest.

The court, sitting in Cairo for security reasons, also handed down life sentences to five defendants, with 19 receiving lesser jail terms and another 28 exonerated.

Palestinian factions meeting in Cairo wrapped up two days of talks aimed at reconciling the rival Hamas and Fatah late on Saturday although divisions remained over how exactly to apply the deal, an official said.

The talks, which began on Friday, were held under the umbrella of the provisional governing body of the Palestine Liberation Organization (PLO).

Egyptian security used water cannon and fired shots into the air as protesters threw petrol bombs and stones into the grounds of the presidential palace in Cairo on Friday, an AFP correspondent said.

The clashes came amid rallies in several cities against Islamist President Mohammed Morsi following unrest that killed 56 people, mostly in Port Said, after 21 residents were sentenced to death over a football-related riot in 2012.

Two people died in clashes between protesters and police near Cairo's Tahrir Square on Wednesday, medics said.

Both of the victims, neither of whom was identified, were hit by buckshot.

Egyptian President Mohammed Morsi has appealed for calm after seven people died in clashes between police and protesters on the second anniversary of the revolt that toppled Hosni Mubarak.

As troops were deployed in the flashpoint city of Suez, Morsi, in a message posted on his Twitter account Friday, urged "citizens to adhere to the values of the revolution, express opinions freely and peacefully and renounce violence".