Pope Leo says he is deeply concerned about rising tensions between the United States and Cuba, and he called for “sincere and effective dialogue” to prevent violence and further suffering for the Cuban people.

U.S. President Donald Trump said last week that tariffs would be imposed on imports from countries that supply Cuba with oil, ratcheting up the pressure on Washington’s long-time foe after ousting Venezuelan President Nicolas Maduro, a key Cuban ally, in early January.

Pope Leo said he had received reports “with great concern” of rising tensions between Cuba and the United States. He joined Cuban bishops in “urging those responsible to promote sincere and effective dialogue to avoid violence and further suffering for the Cuban people,” in comments after his weekly Angelus prayer.

Cuba’s Foreign Minister Bruno Rodriguez declared an “international emergency” in response to the U.S. tariff warning, which he said constituted “an unusual and extraordinary threat.”