BRUSSELS — Just hours before President Trump declared Jerusalem the capital of Israel, prompting warnings of unrest across the Muslim world, the administration’s top diplomat said on Wednesday that peace in the Middle East was still possible.

Secretary of State Rex W. Tillerson, during a news conference at NATO headquarters in the heart of Europe, said that he did not want to pre-empt the president’s official announcement, but expressed reassurances about the expected consequences of the decision.

“The president’s very committed to the Middle East peace process,” Mr. Tillerson said.

Mr. Tillerson has been largely shut out of the usual back-and-forth between Israelis and Palestinians that many secretaries of state spent much of their tenures conducting. Instead, Mr. Trump entrusted that task to his son-in-law and senior adviser, Jared Kushner.

In his remarks on Wednesday, Mr. Tillerson was complimentary toward Mr. Kushner’s Middle East peace efforts, which have also been pursued by Jason Greenblatt, an assistant to the president.