Three people were killed in Egypt Friday in clashes between supporters and opponents of deposed president Mohammed Morsi, and police arrested dozens of Islamists across the country, security officials said.

A police officer said a street vendor was shot dead in clashes between Morsi's Islamist supporters and civilian opponents in the Mediterranean city of Alexandria.

Egypt extended Thursday by 15 days the detention of three journalists working for Al-Jazeera television network who the authorities accuse of threatening public order, one of their lawyers said.

Australian Peter Greste, the Canadian-Egyptian bureau chief for Jazeera English in Cairo Mohammed Fahmy and producer Baher Mohamed, were arrested on December 29 in a Cairo hotel.

Courts on Thursday jailed 87 supporters of Egypt's deposed President Mohammed Morsi to three years for taking part in unauthorized and violent protests, judicial sources said.

One Cairo misdemeanor court condemned 63 supporters of the Islamist to three years in prison and fined them 50,000 Egyptian pounds ($7,200, 5,250 euros) over protests in November, the officials said.

Muslim Brotherhood-linked cleric Yusef al-Qaradawi has issued a religious decree prohibiting Egyptians from voting in a referendum to be held next week by the military-installed interim government.

Islamist supporters of deposed president Mohamed Morsi had already called for a boycott of the January 14-15 vote on a new constitution drawn up by the interim authorities since his July overthrow by the army.

An Egyptian court on Wednesday adjourned the murder trial of deposed President Mohammed Morsi to February 1, citing "weather conditions" that prevented the Islamist's transport to court from prison.

It had been scheduled as the second hearing in Morsi's trial, after an initial court appearance in November in which he denounced the tribunal and insisted he was still the country's president.

A fiery hot air balloon crash in Egypt last year that killed 19 tourists was probably caused by a gas leak, an official Egyptian report released on Tuesday said.

The accident took place on the morning February 26, soon after the balloon lifted off in the southern city of Luxor.

Lawyers for the Muslim Brotherhood have submitted a complaint to the ICC asking it to investigate the military's alleged crimes against humanity in Egypt, they said in London on Monday.

Lawyers acting for the Brotherhood's Freedom and Justice Party said they hoped to meet with the International Criminal Court prosecutor in the coming months to discuss opening a preliminary investigation.

Egypt summoned Iran's envoy in Cairo on Monday to protest Tehran's criticism of deadly clashes between police and Islamist protesters, the foreign ministry said.

The envoy was told to relay "a strongly worded message" to Tehran, Egyptian foreign ministry spokesman Badr Abdelatty told Agence France Presse.

An Egyptian court on Sunday gave suspended one-year sentences to 12 activists including youth leaders of the 2011 uprising for an attack on a former presidential candidate's headquarters.

Those sentenced include Alaa Abdel Fattah and Mona Seif, prominent youth activists known for their leading role in the revolt that toppled president Hosni Mubarak.

Egypt's interim president on Sunday made a rare visit to see the pontiff of the nation's Orthodox Christians at St. Mark's Cathedral, the papal seat in central Cairo, according to a brief statement by the church.

The highly symbolic visit to Pope Tawadros II by Adly Mansour was made ahead of the Coptic Christmas, which falls on Tuesday.