(Reuters) - A Russian airliner that crashed in Egypt's Sinai Peninsula broke up in midair, an official of a Moscow-based aviation agency said on Sunday after visiting the disaster site, but stressed it was too early to draw conclusions from this. Russian authorities also ordered Kogalymavia airline, operator of the Airbus A321 which came down on Saturday killing all 224 people on board, not to fly its jets of the same model until the causes of the crash are known.

The jet, which Kogalymavia flew under the brand name Metrojet, was carrying holidaymakers from the Red Sea resort of Sharm el-Sheikh to St. Petersburg when it crashed into a mountainous area of central Sinai shortly after losing radar contact near cruising altitude.

"The destruction happened in the air, and fragments were scattered over a large area of around 20 square kilometers," said Viktor Sorochenko, director of the Intergovernmental Aviation Committee. However, he warned against reading anything into this information. "It's too early to talk about conclusions," he said on Russian television from Cairo.

The Moscow-based committee represents governments of the Commonwealth of Independent States, which groups Russia and other former Soviet republics.

Egyptian analysts began examining the contents of the two "black box" recorders recovered from the airliner although the process, according to a civil aviation source, could take days. However, Russian Transport Minister Maxim Sokolov told Russia 24 television that this work had not yet started.

At St. Petersburg's Pulkovo Airport on Sunday, grieving Russians piled flowers high in memory of their dead compatriots. Mourners in Moscow arranged candles to spell out 7K-9268, the number of the flight that crashed.

Carriers from United Arab Emirates, Qatar, Bahrain and Kuwait said they would re-route flights over Sinai as a security precaution until there was more clarity. Abu Dhabi's Etihad Airways said it would continue to overfly the peninsula but avoid airspace over certain areas on the advice of Egyptian authorities.

Months Of Inquiries

A militant group affiliated to Islamic State in Egypt said in a statement that it brought down the plane "in response to Russian airstrikes that killed hundreds of Muslims on Syrian land", but Sokolov told Interfax news agency the claim "can't be considered accurate."

Egyptian President Abdel Fattah al-Sisi said it could take months to establish the truth behind the crash though his country was cooperating with Russia to aid investigations.

"This is a complicated matter and requires advanced technologies and broad investigations that could take months," Sisi said in a televised speech on Sunday.

The wreckage was found in a desolate area of stony ground.

Rescuers had collected the colorful suitcases of the passengers into a pile. A pink child's sandal decorated with white flowers lay among the debris, a reminder that 17 children were among those killed as they headed home from their holidays.

Parts of the wreckage were blackened and charred, with one section forming heaps of twisted metal, although the blue Metrojet logo was still visible on its broken tail fin.

As the Russian investigators moved slowly across the site, Egyptian military helicopters buzzed overhead, combing the wider area for debris -- or bodies -- not yet found.

At least 163 bodies had already been recovered and transported to various hospitals including Zeinhom morgue in Cairo, according to a cabinet statement.

Airport security sources said Russian experts who arrived on Saturday brought with them refrigerators and DNA samples to help identify and take home the dead.

Russian experts had already visited the morgue on Saturday night and Moscow's ambassador to Cairo said the first 130 bodies were due to leave on Sunday evening bound for St. Petersburg.

A source inside the morgue said the bodies had been numbered using bracelets, ready to be received by the Russians, and empty ambulances were arriving to pick them up.

Those on board the doomed flight included 214 Russians, at least three Ukrainians and one Belarusian, most returning from the Red Sea, popular with Russians seeking winter sun.

The Russian flag was flying at half-mast over the country's embassy in Cairo on Sunday morning. President Vladimir Putin has declared a day of national mourning in Russia.

Russia's transport regulator said in a statement that it had grounded Kogalymavia's Airbus A321s until the reasons for the crash became clear.

Russian transport prosecutors have already examined the quality of the fuel used by the airliner and found that it met necessary requirements, Russia's state-run RIA news agency said.

The crew had also undergone medical tests recently and no problems were detected, Interfax reported.

Experts from Airbus have begun arriving in Egypt to assist in the investigation, the civil aviation ministry said.