Egypt on Tuesday referred Muslim Brotherhood leader Mohamed Badie to trial for staging a protest at a Cairo square where several police and hundreds of Islamist protesters were killed in 2013 clashes.

Badie, who has already been sentenced to death in two other trials, was charged in connection with the killing of policemen when security forces dispersed the protest at the capital's Rabaa al-Adawiya Square on August 14, 2013.

A small bomb exploded Monday near a traffic post in the Egyptian capital wounding four policemen, two of them seriously, in an attack claimed by a Cairo-based militant group.

Jihadists have launched a wave of attacks targeting security forces since the ouster of Islamist president Mohamed Morsi in 2013. 

Egypt Monday postponed again its verdict in the trial of the brother of the Al-Qaida chief but sentenced 10 co-defendants to death for forming a "terrorist group", a court official said.

The verdict against Mohamed al-Zawahiri, whose brother Ayman al-Zawahiri heads the global jihadist network, was postponed until September 27.

Twenty-one people have died and 66 others were hospitalized with exhaustion as soaring temperatures and high humidity hit Cairo and other parts of Egypt, the health ministry said Monday.

The victims, who all died on Sunday, succumbed as temperatures reached highs of 47 degrees Celsius (117 Fahrenheit), in conditions made less bearable by elevated humidity levels.

A prominent leader of a hardline Islamist group that backed ousted Egyptian president Mohamed Morsi has died in jail in Cairo, the interior ministry said on Sunday.

It said Essam Derbala, a senior leader in Gamaa Islamiya, died on Saturday after returning from a hearing at his trial.

Gunmen killed an Egyptian policeman southwest of Cairo on Saturday, the interior ministry said.

The assailants were hiding in a field and fired on a convoy transporting two prisoners due for release, before fleeing the scene, a police general told AFP.

Fears mounted Friday over the fate of a Croatian abducted near Cairo by Islamic State group militants who have threatened to execute him unless Muslim women in Egyptian jails are freed.

Croatian President Kolinda Grabar-Kitarovic said she would talk to her Egyptian counterpart Abdel Fattah al-Sisi by telephone as the 48-hour deadline set by the jihadists on Wednesday neared.

President Abdel Fattah al-Sisi unveiled an expanded Suez Canal Thursday in a lavish ceremony, with the first ships passing through the waterway in what Egypt hopes will boost its economy and global standing.

Sisi, dressed in a ceremonial military uniform, arrived aboard a historic yacht at the head of a naval flotilla as fighter planes and helicopters flew overhead.

Speaker Nabih Berri, Prime Minister Tammam Salam and Deputy PM Defense Minister Samir Moqbel attend Thursday the inauguration of a major extension of the Suez Canal in Egypt.

The three officials are expected to return to Beirut the same day.

Egypt's affiliate of the Islamic State group threatened Wednesday to execute a Croatian kidnapped in Cairo last month within 48 hours if Muslim women jailed in Egypt are not freed.

The man is the first foreigner to be abducted and threatened with death by militants in Egypt since an Islamist insurgency erupted two years ago.