The following is a declaration of Vatican spokesman Fr. Federico Lombardi issued Monday evening regarding the killing of three Israeli youth:

"The news of the killing of three young Israelis who had disappeared is terrible and dramatic. The assassination of innocent persons is always despicable and unacceptable, and a very serious obstacle to that peace to which we must continue untiringly to commit ourselves and for which we must pray. Violence calls for more violence and feeds the mortal circle of hatred. Pope Francis unites himself to the indescribable pain of the families stricken by this homicidal violence and to the pain of all people stricken by the consequences of hatred, and asks God to inspire in all thoughts of compassion and peace."

The three teens -- Eyal Yifrach, 19; Gilad Shaar, 16; and Naftali Frenkel, a 16-year-old dual U.S.-Israeli citizen -- disappeared late June 12 or early June 13 from the Jewish settlement of Gush Etzion in the West Bank, according to the Israeli military.

Israel has vowed retribution against Hamas, the militant Palestinian group it accuses of the kidnap and murder of the three youths.

Overnight, Israel launched more than 30 air strikes on the Gaza Strip. The strikes came in response to 18 rocket attacks on southern Israel from Gaza since Sunday night, the Israeli military said.