Nearly two dozen U.S. senators sent a letter to President Trump demanding an investigation into the disappearance of prominent Saudi journalist Jamal Khashoggi and threatening possible sanctions against his alleged attackers.

The letter, signed by all but one member of the Senate Foreign Relations Committee, signaled their intent to push for a U.S. response to the disappearance of Mr. Khashoggi.

Mr. Khashoggi hasn’t been seen since last week, when he entered the Saudi consulate in Istanbul to obtain documents to marry his Turkish fiancée. His disappearance has sparked a diplomatic crisis between Turkey and Saudi Arabia. Turkish officials have said they believe he was killed. Saudi officials have denied involvement and say they are assisting the Turkish investigation into Mr. Khashoggi’s disappearance.

President Trump on Wednesday stepped up pressure on Saudi Arabia over Mr. Khashoggi’s disappearance, calling it a “very bad situation.”

“We cannot let this happen. To reporters, to anybody,” Mr. Trump told reporters in the Oval Office. “We’re going to get to the bottom of this.”