Pope Francis this week extended his condolences and prayers for the victims of a deadly bus crash in Venice, Italy, the Vatican said in a bulletin on Thursday.

The Holy See Press Office said in a release that the Holy Father had dispatched a “telegram of condolence” to those who had been affected by the Tuesday crash, which occurred when a bus ran off an overpass in the Venetian borough of Mestre.

Authorities reported that the bus broke out in flames after crashing. At least 21 people were reported dead by Friday morning, with nearly as many injured.

In the telegram, addressed to Patriarch of Venice Francesco Moraglia, Vatican Secretary of State Cardinal Pietro Parolin said that “having learned of the serious road accident that occurred in Mestre, in which several people lost their lives, including children,” Francis asked Patriarch Moraglia “to convey his affectionate proximity to the families of those who died so tragically.”

The Pope “assur[ed] them of a special prayer for their repose,” Cardinal Parolin said, “and as he implores the consolation of faith for the relatives, he invokes from the Lord prompt healing for the injured and sends his heartfelt paternal apostolic blessing.”

The cause of the crash was as of Friday morning still unclear. Luca Zaia, the president of the Veneto region of Italy of which Venice is the capital, told the state-owned Radiotelevisione Italiana that it was “difficult to understand how it happened.”

“The bus was new and electric, and that street wasn’t particularly problematic,” Zaia told RAI.

The president said elsewhere that authorities were assuming the bus driver had “fallen ill” before the crash, according to Reuters.

The bus was reportedly carrying foreign tourists to a camping site.