Russian passenger plane that crashed in Egypt's Sinai Peninsula, killing all 224 people on board, broke apart in mid-flight, Russian official says. 

International investigators on Sunday began probing why the plane crashed as rescue workers widened their search for missing victims.

"It is too early to speak about the crash causes," said the Chief of Russia's Interstate Aviation Committee, Viktor Sorochenko, after examining the site of the wreckage, according to the TASS news agency. 

"The plane broke down in midair, and its fragments are scattered over a vast area of about 20 square kilometres," he said. 

The bodies of 179 of the victims were flown home from Cairo airport late on Sunday, accompanied by Russian Transport Minister Maxim Sokolov. 

An Egyptian civil aviation official said Russian search and rescue teams on Monday would resume combing the crash site in Sinai's remote desert interior for the bodies of the remaining victims. 

Russia mourns victims 

Russia mourned the victims of its biggest-ever air disaster after the passenger jet full of Russian tourists crashed.

Flags were at half-mast on Sunday at the parliament building, the Kremlin, and other official buildings in honour of the victims, most of whom were from Russia's second-largest city of St Petersburg.

The Airbus A321-200, operated by the Moscow-based Metrojet airline, crashed in a remote mountainous part of the Sinai Peninsula 23 minutes after taking off from Sharm el-Sheikh on Saturday morning.

The plane was flying to St Petersburg carrying mainly Russian tourists returning from holidays in the popular Red Sea resort.

Sharm al-Sheikh, one of Egypt's biggest resorts, is very popular with Russians. Strung out along some 30 kilometres of Red Sea coast, it boasts sandy beaches, well-known scuba diving sites and lively nightclubs. 

Ukrainians lay flowers and light candles in memory of victims at the Russian embassy in Kiev, Ukraine [Sergey Dolzhenko/EPA]

Many entertainment venues in Moscow cancelled their programmes, and media organisations turned their social network icons monochrome as a mark of respect.

President Vladimir Putin, whose office announced a day of national mourning, was, however, absent from the screens, and some Russians criticised him for failing to speak to the nation about the tragedy.

Source: Agencies