President Trump has decided not to sign onto a statement calling for de-escalation between Iran and Israel that is being prepared by the Group of 7 industrialized nations, according to a White House official, the first evidence of an ongoing rift between Mr. Trump and his fellow leaders gathered for a summit in Alberta, Canada.

The official, who asked for anonymity to discuss the joint statement, which has not been released publicly, did not say why the president was opposed to signing. A copy of the draft statement, which was obtained by The New York Times, urges both Israel and Iran to halt attacks on one another, which have killed dozens of people in both countries over the past several days.

A G7 official said the draft statement was not final and that discussions about the situation in the Middle East among the leaders, including Mr. Trump, were expected to continue throughout the day on Monday and again on Tuesday. The official requested anonymity to discuss a sensitive diplomatic matter.

The draft statement expresses deep concern regarding the conflict, which began on Friday when Israel launched strikes across Iran, including on its nuclear research facilities. The Israeli prime minister, Benjamin Netanyahu, has said the strikes are necessary to prevent Iran from developing a nuclear weapon.

The Israeli strikes prompted waves of retaliatory ballistic missiles and drones from Iran, some of which struck targets across Israel. Iran has repeatedly said it does not intend to build a nuclear weapon but insists on being allowed to develop nuclear power for the country’s needs.

The draft G7 statement is being prepared for the leaders of the group’s member nations — besides the United States and Canada, they are Britain, France, Germany, Italy, Britain, Japan and the United States — along with the leaders of the European Union. It acknowledges the need to prevent Iran from acquiring a nuclear weapon and explicitly supports Israel’s right to defend itself.