President Obama has reaffirmed a 4-decade-old secret understanding that has allowed Israel to keep a nuclear arsenal without opening it to international inspections, three officials familiar with the understanding said.

The officials, who spoke on the condition that they not be named because they were discussing private conversations, said Mr. Obama pledged to maintain the agreement when he first hosted Israeli Prime Minister Benjamin Netanyahu at the White House in May.

Under the understanding, the U.S. has not pressured Israel to disclose its nuclear weapons or to sign the nuclear Non-Proliferation Treaty (NPT), which could require Israel to give up its estimated several hundred nuclear bombs.

Israel had been nervous that Mr. Obama would not continue the 1969 understanding because of his strong support for nonproliferation and priority on preventing Iran from developing nuclear weapons. The U.S. and five other world powers made progress during talks with Iran in Geneva on Thursday as Iran agreed in principle to transfer some potential bomb fuel out of the country and to open a recently disclosed facility to international inspection.