Top Trump administration officials defended U.S. backing of the Saudi-led campaign in Yemen on Wednesday and dismissed any connection between Saudi Arabia’s crown prince and a journalist’s murder.

Addressing reporters after briefing the Senate on the situation in Yemen, Secretary of State Mike Pompeo said a planned Senate vote to end U.S. support for the Saudi-led coalition is "poorly timed" and would undermine efforts by UN special envoy to Yemen Martin Griffiths to bring together both sides in the conflict to reach a ceasefire.

"It would encourage the Houthis. It would encourage the Iranians. It would undermine the fragile agreement for everyone to go to Sweden and have this discussion," Pompeo said.

Yemen has been wracked by violence since 2014 when the Houthi rebel group overran much of the country and the crisis escalated in 2015 when a Saudi-led coalition launched a devastating air campaign aimed at rolling back Houthi gains.

Tens of thousands of people, including civilians, are believed to have been killed and the UN estimates that around 14 million Yemenis are at risk of famine.

Defense Secretary James Mattis also defended U.S. support for the war, saying Washington was working to stop Iranian influence in Yemen and that measures were added to enhance the coalition's targeting systems to minimize civilian casualties.

"It is in our interests to end the civil war, to counter Iranian influence and stop Iranian-supplied Houthi rocket and unmanned aerial vehicle attacks on the UAE and Saudi Arabia and their civilian populations," he said in the briefing to senators.

Pompeo also said there was no direct evidence that Saudi Crown Prince Mohammed bin Salman ordered the murder of Saudi journalist Jamal Khashoggi following reports that the CIA had concluded with high confidence that the crown prince did in fact do so.

Mattis added to this, saying "we have no smoking gun that the crown prince was involved".

Khashoggi, a Saudi journalist and columnist for The Washington Post, went missing after entering the Saudi Consulate in Istanbul on Oct. 2.

After initially saying he had left the consulate alive, Saudi Arabia admitted weeks later that he was killed there.

Senators voiced their reactions to the briefing, saying they did not find it convincing while noting that CIA Director Gina Haspel was absent.

Democratic Senator Bob Menendez said Haspel’s absence was an attempt to "stonewall" the Senate.

"We also have a crown prince that is out of control... I don’t think there’s anybody in the room that doesn’t believe that he was responsible for it," said Senator Bob Corker.