ISTANBUL — A suicide bomber struck at the heart of Istanbul’s most popular avenue on Saturday, killing at least four people, including two Americans, and wounding 36, officials said.

A spokesman for the State Department, John Kirby, confirmed on Saturday afternoon that two American citizens, Yonathan Suher and Avraham Goldman, had been killed. No other details were available.

Earlier, Prime Minister Benjamin Netanyahu of Israel announced that two Israelis had died in the blast, and that a third Israeli might also be among the dead, but he did not give their names. Emmanuel Nahshon, the spokesman for Israel’s foreign ministry, later confirmed that two of the victims held dual Israeli-American citizenship. He was presumably referring to Mr. Suher and Mr. Goldman, but Israel had not yet released their names.

In addition, 11 Israelis were wounded, Israeli officials said. Mr. Netanyahu said there was no immediate evidence that the attack had been aimed at Israelis.