Pope Francis, leader of the Roman Catholic Church, offered his condolences Sunday to the victims of a Russian passenger plane crash in Egypt Saturday, which killed 224 people. Francis was the latest world leader to pray for the victims, while authorities continued to discover new information regarding the cause of the crash.

The pope gave victims and their families "the assurance of his prayers," according to a statement from the Vatican, the New York Times reported Sunday. After having "learned with sadness about the tragic crash," the pope sent a telegram to offer his condolences to Russian President Vladimir Putin, according to the same statement.

Francis’ prayers were in response to the fatal incident Saturday when a passenger plane carrying 224 people from Egypt to Russia crashed over the Sinai peninsula in Egypt Saturday, killing everyone onboard. Allies of the Islamic State group in Egypt took credit for the crash, saying they shot down the plane in a statement posted to Twitter.

Russia has been conducting airstrikes against the Islamic State in Syria since Sept. 30, and the Islamic State supporters said they shot down the plane "in response to Russian airstrikes that killed hundreds of Muslims on Syrian land." The terror group and its allies have taken credit for plane crashes from technical difficulties in the past, however, and authorities are still searching for evidence to determine the exact cause of the crash. 

New clues continued to surface Sunday. The plane broke in two in mid-air, according to a statement released by Russian transport officials Sunday. The statement from the Russian transport authority said it was too early to say with certainty what caused the crash, however.

As officials both in Egypt and Russia continued to search for evidence, Russians throughout the nation and the world joined in mourning the 224 lives lost. Putin declared Sunday a national day of mourning for the entire country, with mourning to continue in St. Petersburg, home to most of the victims, in the days to come.

Flags were flying at half-mast and Russian Orthodox priests conducted services to pray for the victims and their families, as the nation grieved its worst airline tragedy in history.