Hours before holding a joint prayer session for peace with Palestinian leader Mahmoud Abbas, President Shimon Peres lambasted a recently reached Palestinian unity agreement Sunday, saying it was doomed to fail.

Peres and Palestinian Authority President Abbas are slated to hold a special prayer for peace with Pope Francis at the Vatican late Sunday afternoon, an initiative pushed by the Vatican during Francis’s visit to the Holy Land two weeks ago.

Remarking on the Palestinian unity government, jointly backed by the Islamist Hamas and Abbas’s more moderate Fatah group, Peres called it a “contradiction that won’t last.”

“One is in favor of terror and one is against terror. That won’t work,” he told reporters upon arriving in Rome Sunday morning. “You can’t have water and fire in the same glass.”

On Monday, Abbas swore in a new unity government supported by Hamas, considered a terror group by Israel and much of the West.

Israel has boycotted the government and called on the international community to do the same, but the US and Europe both said they would work with the new Palestinian leadership.

Ahead of the prayer session, Peres, Abbas and Francis will meet at the pope’s Vatican City residence. Peres, however, downplayed the political aspects of the trip.

“I don’t believe that leaders work in a vacuum. They are influenced both by reality and by spiritual and psychological reality. Therefore — while I don’t think that this has the significance of political negotiations, it has a lot of importance in the broader sense of the attempt to bring peace.”

The prayer session will feature opening remarks followed by Jewish, Christian and Muslim prayers on creation, forgiveness and peace. Following the benedictions, Francis, Peres and Abbas will speak.