Unidentified gunmen killed 16 people and wounded 200 others when they opened fire at a Cairo rally supporting embattled Egyptian President Mohammed Morsi, health ministry officials said Wednesday.

"Sixteen people have been killed and 200 wounded in an attack on a demonstration supporting President Morsi next to Cairo University," state television reported, citing the ministry.

Security forces have arrested eight people in connection with the brutal killing of four Egyptian Shiites in a village south of Cairo, officials said on Tuesday.

"Security efforts have been increased to find the rest of the perpetrators after they fled their homes," a security official told the national MENA news agency.

Egyptian President Mohammed Morsi has repeated a call for dialogue with the opposition in an attempt to mitigate deep political divisions ahead of planned rallies later this month calling for his resignation.

"I have said it before. I urge everyone to sit together to discuss what would achieve the interests of our nation," Morsi said in an interview published in the state-owned Akhbar al-Youm newspaper.

Egyptian Islamists gathered for a show of strength in Cairo on Friday ahead of planned opposition protests calling for President Mohammed Morsi to step down, highlighting the tense political divide in the Arab world's most populous state.

Dozens of parties including Morsi's Freedom and Justice Party -- the political arm of the powerful Muslim Brotherhood -- have called for a demonstration outside the Rabaa al-Adawiya mosque in Cairo's Nasr City neighborhood after noon prayers.

 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.