An initial probe into a hot air balloon crash that killed up to 19 tourists in Egypt has ruled out any criminal activity as a cause of the accident, the official MENA news agency reported on Wednesday.

"Investigations so far by the general prosecution show no suspicion of criminal activity," MENA said, citing the preliminary findings of the investigation into Tuesday's accident at the Egyptian temple city of Luxor.

Egypt's main opposition coalition, the National Salvation Front, said Tuesday it will boycott upcoming parliamentary elections due to a lack of guarantees of a transparent process.

"The decision of the Front, unanimously, is to boycott the elections," NSF member Sameh Ashour told a news conference in Cairo after a meeting of the alliance grouping mainly liberals and leftists.

A hot air balloon exploded and plunged to earth at Egypt's ancient temple city of Luxor during a sunrise flight on Tuesday, killing up to 19 tourists, including Asians and Europeans, sources said.

The balloon carrying 21 tourists from Hong Kong, Japan, France, Britain and Hungary was flying at 300 meters (1,000 feet) when it exploded and caught fire, a security official said.

A controversial Egyptian Islamist was freed on bail on Monday after he was held in custody for four days on charges of insulting Christianity, a judicial official said.

Ahmed Abdullah, an extremist preacher also known as Abu Islam, was arrested after Coptic Christian activist Nagib Gibrail accused him of insulting Christianity on a television show.

Egyptian President Mohammed Morsi on Monday called for a meeting with the country's opposition to discuss upcoming legislative polls, amid calls for a boycott.

"I call on all the brothers in the different parties in all of Egypt to come... so we can sit and put in the place the guarantees for the transparency and fairness of the elections," Morsi said in an interview on private satellite channel al-Mehwar.

Opposition leader Mohamed ElBaradei on Saturday called for a boycott of Egypt's upcoming legislative elections, as the president rescheduled the first round after Copts complained it would clash with a Christian holiday.

"Called for parliamentary election boycott in 2010 to expose sham democracy. Today I repeat my call, will not be part of an act of deception," the Nobel Peace laureate and former head of the U.N. atomic watchdog wrote on Twitter.

Protesters on Sunday blocked the doors to Cairo's main administrative building as part of a growing campaign of civil disobedience around the country against Islamist President Mohamed Morsi.

A group of protesters closed the doors of the Mugamma, a massive labyrinth of bureaucratic offices on the edge of Tahrir Square, leaving only a side exit for employees to leave, employees told Agence France Presse.

Egyptian police said Saturday they have arrested four students who filmed themselves publicly dancing in their underwear, as more people around the world emulate a viral dance craze called the "Harlem Shake."

The four pharmaceutical students shocked residents of a middle class Cairo neighborhood when they removed most of their clothes and videotaped themselves performing the pelvis-thrusting dance, a police official said.

Opponents of Egypt's President Mohamed Morsi are voting to send him where no Islamist leader has gone before: outer space.

Morsi on Saturday was leading the field in Egypt in an online contest sponsored by deodorant makers Axe to send a lucky few on a shuttle operated by space tourism company Space Expedition Corp.

Human Rights Watch on Saturday urged authorities in the United Arab Emirates either to charge a group of Egyptians held over suspected links with Egyptian President Mohammed Morsi's Muslim Brotherhood or release them.

"If the UAE government can show the Egyptian detainees have engaged in criminal behavior, why hasn't it charged them with a crime," asked Nadim Houry, HRW's deputy Middle East director.