WASHINGTON (AP) — President Donald Trump suggested Monday that "rogue killers" could be responsible for a Saudi journalist's disappearance after a personal phone call in which Trump said Saudi Arabia's King Salman strongly denied any knowledge of what happened to Jamal Khashoggi.

Trump also announced he'd dispatched Secretary of State Mike Pompeo to the Kingdom — and anywhere else necessary — to get to the bottom of the suspected murder of Khashoggi, who hasn't been seen since entering the Saudi consulate in Istanbul two weeks ago.

The U.S. president is under growing pressure to take action on the suspected murder of the Saudi writer, who has been living and working in the United States, including contributing to The Washington Post and writing columns critical of Saudi Crown Prince Mohammed bin Salman. Turkish officials say they believe Saudi agents killed and dismembered Khashoggi and Turkey has audio and video recordings of it.

Trump said Monday he had spent about 20 minutes on the phone with King Salman, who denied having any information about what had happened to Khashoggi.

"The king firmly denied any knowledge of it," Trump told reporters as he left the White House for a trip to survey hurricane damage in Florida and in Georgia. Trump said he didn't "want to get into (Salman's) mind," but told reporters: "it sounded to me like maybe these could have been rogue killers. I mean, who knows? We're going to try getting to the bottom of it very soon, but his was a flat denial."

In Istanbul, meanwhile, Turkish and Saudi investigators were to begin conducting a joint inspection of the consulate. A team arrived by unmarked police cars at the consulate but said nothing to journalists waiting outside as they entered the building.

The kingdom has called the allegations of foul play "baseless" but has offered no evidence the writer left the consulate.

Trump tweeted early Monday that Salman denied any knowledge of "whatever may have happened 'to our Saudi Arabian citizen.'"

He made that point again and again as he left the White House, telling reporters, "All I can do is report what he told me."

"His denial to me could not have been stronger," Trump said, echoing language he has used to describe Russian President Vladimir Putin's denials of meddling in the 2016 election that sent Trump to the White House. U.S. intelligence officials have reported they are certain the interference took place in an effort to hurt Hillary Clinton's campaign.

Trump promised "severe punishment" for whoever was to blame in a "60 Minutes" interview that aired Sunday. But he has said repeatedly that he does not want to halt a proposed $110 billion arms sale to Saudi Arabia — as some in Congress have said he should — because it would harm the U.S. economically..

Saudi Arabia has pledged to retaliate economically for any U.S. punitive action.

Trump said he'd made clear the stakes.

"The world is watching, the world is talking. This is very important to get to the bottom of it," Trump said. "I think he understands that very well."

Treasury Secretary Steven Mnuchin still plans to attend a previously scheduled Saudi conference this week to address terrorist financing, but those plans could change as the investigation progresses, said White House economic adviser Larry Kudlow.

Sens. Marco Rubio and Jeff Flake, members of the Foreign Relations Committee, have said Congress is prepared to move quickly and firmly if Trump fails to adequately respond to Khashoggi's disappearance. Rubio said Sunday that U.S.-Saudi relations may need to be "completely revised."

"There's not enough money in the world for us to buy back our credibility on human rights if we do not move forward and take swift action," Rubio said on CBS' "Face the Nation."

More than 20 Republican and Democratic senators instructed Trump last week to order an investigation into Khashoggi's disappearance under legislation that authorizes sanctions for perpetrators of extrajudicial killings, torture or other gross human rights violations.

Khashoggi had been living in self-exile in Virginia for the past year.

Trump visited the kingdom on his first overseas trip as president and his son-in-law and senior adviser Jared Kushner has forged close ties with Crown Prince Mohammed bin Salman.