The US Senate has delivered back-to-back votes against Saudi Arabia and a rare rebuke of President Donald Trump's response to the killing of US-based journalist Jamal Khashoggi, signalling new scepticism from Capitol Hill toward the longtime Middle East ally.

Key points: Senate passes resolutions despite Trump administration's attempts to torpedo them

Republican senator describes Saudi Crown Prince as "toxic" and "flawed"

The US must respect human rights over economic arguments, the senate voted

Although the resolutions are largely symbolic, as it's unclear if they will be considered by the House, their passage demonstrated that senators were seeking to assert oversight of the Trump administration's foreign policy and its relationship with Saudi Arabia.

It also marked the collapse of the Trump administration's effort in the Senate to contain fallout from the gruesome killing.

Saudi journalist Jamal Khashoggi was killed at the Saudi Arabian consulate in Istanbul in October. ( Supplied: Time )

One measure recommended that the US end its assistance to Saudi Arabia for the war in Yemen.

Human rights groups have reported that the war is wreaking havoc on the country and subjecting civilians, many of them children, to deadly disease and indiscriminate bombing.

The other put the blame for the death of Khashoggi firmly on Saudi Crown Prince Mohammed bin Salman.

Both had been vigorously opposed by the Trump administration, which threated a potential presidential veto.

"The current relationship with Saudi Arabia is not working," Senator Lindsey Graham said.

He opposed the Yemen resolution but called the Crown Prince "so toxic, so tainted, so flawed" after Khashoggi's killing, that "you're never going to have a relationship with the United States Senate unless things change".

The bipartisan votes came two months after the Saudi journalist's slaying at the country's consulate in Istanbul and after Mr Trump persistently equivocated over who was responsible.

US intelligence officials concluded that the Crown Prince must have at least known of the plot, but Mr Trump has repeatedly praised the kingdom.

Senators made it clear where, and who, they put the blame on.

The resolution, passed by unanimous agreement, says the Senate believes the Crown Prince is "responsible for the murder" and called for the Saudi Arabian government to "ensure appropriate accountability".

Resolution a 'historic moment'

Senators voted 56-41 to recommend that the US stop supporting the war in Yemen, a direct affront to the administration's war powers abilities.

Independent Senator Bernie Sanders, who co-sponsored the Yemen resolution with Republican Senator Mike Lee, called passage a "historic moment".

Mr Lee said Khashoggi's death focused attention "on the fact that we have been led into this civil war in Yemen half a world away" and "we've done so following the lead" of Saudi Arabia.

"What the Khashoggi event did was to demonstrate, hey, maybe this isn't a regime that we should just be following that eagerly into battle," Mr Lee said.

As Senate approval loomed, the administration dispatched Secretary of State Mike Pompeo and Defence Secretary Jim Mattis to the House to make the case against the resolutions and warn of damage they could do to the US-Saudi relationship.

A congressional aide and an administration official said their appearance was aimed at stopping any House action on the resolutions.

Mr Pompeo and Mr Mattis had made a similar entreaty to the Senate late last month.

Mr Trump's support is seen as crucial in the rise of Mohammed bin Salman and his prospects as Saudi king. ( Reuters: Kevin Lamarque )

But it was roundly panned by senators angered by the secretaries' refusal to accept a CIA determination that assessed the Crown Prince had ordered Khashoggi's murder.

CIA Director Gina Haspel briefed House leaders on Wednesday about Khashoggi's slaying.

The journalist, who had lived in the US and wrote for The Washington Post, had been critical of the Saudi regime. He was killed in what US officials have described as an elaborate plot as he visited the consulate for marriage paperwork.

Saudi prosecutors have said a 15-man team sent to Istanbul killed Khashoggi and then dismembered his body, which has not been found.

Those findings came after Saudi authorities spent weeks denying that Khashoggi had been killed in the consulate.

Trump refuses to condemn Saudi over shocking killing

Mr Trump has been reluctant to condemn the Crown Prince, saying that the United States "intends to remain a steadfast partner" of the country, touted Saudi arms deals worth billions of dollars to the US.

But Graham and Senator Bob Menendez, the top Democrat on the Foreign Relations Committee, have rejected Mr Trump's economic arguments; they are setting the stage for legislation next year that goes further in halting arms sales and taking other measures.

Mr Menendez said that economic concerns do not overpower human rights and the US must send a "global message that killing with impunity" will not be tolerated.

The Senate debate came as the United Nations secretary general on Thursday announced that Yemen's warring sides have agreed to a province-wide cease-fire and withdrawal of troops in Hodeida, a contested Red Sea port city.

The agreement came during peace talks in Sweden.

The brutal four-year-old civil war pits the internationally recognised Yemeni government, supported by a Saudi-led coalition, against the Iran-backed rebels known as Houthis.

AP

