Trump 'concerned' about missing Saudi journalist

US President Donald Trump expressed concern on Monday over the disappearance of Saudi journalist Jamal Khashoggi, who was last seen visiting the Kingdom’s consulate in Istanbul.

“I am concerned about it. I don’t like hearing about it. Hopefully that will sort itself out. Right now nobody knows anything about it. But there’s some pretty bad stories going around. I do not like it,” Trump told reporters on the White House lawn as he was returning from a trip by helicopter to Orlando, Florida.

Earlier in the day, senior Republican Senator Lindsay Graham reacted strongly to the news.

Riyadh must provide "honest answers," Graham said on his Twitter account, adding his position is shared by fellow Senators Bob Corker, a Republican, and Ben Cardin, a Democrat.

“We agree if there was any truth to the allegations of wrongdoing by the Saudi government it would be devastating to the US-Saudi relationship and there will be a heavy price to be paid — economically and otherwise," Graham said.

"Our country’s values should be and must be a cornerstone of our foreign policy with foes and allies alike," he added.

Khashoggi, journalist and columnist for The Washington Post, has been missing since he entered the consulate in Istanbul on October 2.

On Monday, Turkish President Recep Tayyip Erdogan urged the Saudi consulate to prove whether or not Khashoggi exited the building after entering, saying the consulate officials "can't get away with [simply] saying 'he left the building'."

Turkish police investigating the case said on Saturday that 15 Saudis, including several officials, arrived in Istanbul on two planes had entered the consulate while Khashoggi was inside.

Istanbul prosecutors are investigating the incident, while the consulate said on Twitter that it was working in coordination with Turkish authorities.

Turkey on Monday said it expects "full cooperation" from Saudi authorities in finding the missing journalist.