Protesters and police clashed again overnight outside Cairo's security headquarters in the wake of deadly football violence and amid calls by activists for civil disobedience in Egypt.

Police fired birdshot at demonstrators in roads leading to the interior ministry, the scene of days of clashes sparked by the deaths of 74 people on Wednesday in football-related violence in the northern city of Port Said.

Egypt is to try 44 people, including Americans, over the funding of non-governmental organizations, a day after the United States said aid to Cairo will be reviewed over the crackdown.

"Forty-four people, including Egyptians, 19 Americans and other nationalities, have been referred to the Cairo criminal court in the NGO funding case," the source told Agence France Presse, adding that a travel ban on all remained in place.

Protesters and riot police fought pitched battles in Cairo Sunday as clashes sparked by the perceived failure of Egypt's military rulers to prevent deadly football-linked violence raged into a fourth day.

Hundreds of riot police blocked roads leading to the Interior Ministry headquarters in the center of the capital, firing tear gas to keep dozens of rock-throwing protesters at bay.

Saboteurs on Sunday blew up a pipeline that supplies gas to Israel, the 12th such attack in a year, security officials said.

Masked gunmen planted explosives under the pipeline in the Al-Massaeed area, close to the town of El-Arish in the north of the Sinai Peninsula, they said.

Police fired tear gas and birdshot at protesters on Saturday in the third day of deadly clashes in Cairo, as anger at the ruling military boiled over after 74 people died in football-related violence.

The police responded after dozens of protesters threw stones at officers guarding the interior ministry headquarters hundreds of meters (yards) from the Egyptian capital's iconic Tahrir Square.

Two Egyptian protesters died on Friday of tear gas inhalation, medics said, as clashes raged in central Cairo between police and protesters amid nationwide protests calling for the ouster of the ruling military amid fury at the deaths of 74 people in football-related violence.

The two were rushed to hospital unconscious after joining protests near the interior ministry where riot police fired tear gas and demonstrators hurled rocks back, after a night of confrontations left hundreds injured.

Two American women and their Egyptian tour guide, who were captured by armed Bedouins in the Sinai peninsula on Friday, have been released unharmed after several hours, security officials said.

The three arrived back at their hotel in the Red Sea resort of Sharm el-Sheikh, where they were met by South Sinai's governor and security chief, officials said.

The Egyptian government sacked the head of security in the northern city of Port Said after an explosion of football violence that left 74 people dead, state media reported Thursday.

Interior Minister Mohammed Ibrahim fired city security chief Essam Samak because of the rioting that erupted late Wednesday seconds after the final whistle at a match between two rival teams, the MENA news agency reported.

At least 74 people were killed and hundreds injured when rival fans clashed Wednesday after a football match in Port Said, highlighting a security vacuum in post-revolution Egypt.

In one of the deadliest incidents in the sport's history, violence erupted as soon as the referee blew the final whistle in a match which saw home team al-Masri beat Cairo's al-Ahly 3-1.

China said Wednesday that 25 Chinese workers kidnapped by Egyptian Bedouins demanding the release of their Islamist relatives had been released.

The incident comes days after 29 Chinese nationals in Sudan were captured by rebels who attacked their camp in the volatile South Kordofan state, where they were involved in a road-building project. They have still not been released.