The US Senate sent a fresh warning to President Donald Trump and Saudi Arabia on Wednesday by greenlighting a vote that could end US military support for Riyadh's war in Yemen, even as UN mediators in Sweden rushed to broker a truce between government representatives and rebels with just hours left before negotiations come to an end.

Anger at the human cost of the war, as well as outrage over the killing of US-based journalist Jamal Khashoggi in the Saudi consulate in Istanbul, have prompted a harder line in Congress about the US military's role in backing the Saudi-led coalition fighting to bolster the Yemeni government against Houthi rebels.

That mounting anger may prompt a separate measure in the coming days accusing Saudi Crown Prince Mohammed bin Salman of direct involvement in the journalist's killing – in line with the reported conclusions of the CIA, whose director Gina Haspel briefed lawmakers on Capitol Hill Wednesday.

That would be a direct challenge to Trump, who has sought to cast doubt on the crown prince's involvement in the killing and has stressed instead the importance of US trade and military ties with the kingdom.

The Senate voted to advance the resolution that ends US backing for the Saudi-led intervention in Yemen by 60 votes to 39, with 11 Republicans joining Democrats to back the measure.

The final Senate vote is expected to take place on Thursday, although even if the upper house approves the resolution, it is likely to run aground in the lower House of Representatives where Republicans hold the majority until January 3.

And even if Congress does back the measure, Trump will be able to deploy his veto power. It remains, however, a powerful symbol of growing unease at US backing for the young heir apparent to the Saudi throne.

Republican Senate majority leader Mitch McConnell – a Trump loyalist – had called on his party to vote against the resolution. But he did back a pending non-binding resolution that would hold the Saudi crown prince responsible for the Khashoggi killing.

That resolution, crafted by Bob Corker, a Republican who has been critical of the president, is expected to enjoy broad bipartisan support.

In the meantime, Secretary of State Mike Pompeo and Defense Secretary Jim Mattis are set to defend the alliance with Riyadh in a closed-door briefing to Congress on Thursday.

UN talks amid famine threat

Related story: Pressure builds on Yemen's warring parties as peace talks to close

Meanwhile, the UN talks that opened last week in Sweden to deal with the crisis in Yemen amid threats of a famine outbreak is scheduled to close on Thursday.

Taiz, the southwestern city controlled by the government and surrounded by the rebels, is no longer under discussion at the talks – the first meeting in two years between Yemen's Houthi rebels and the Saudi-backed government of President Abedrabbo Mansour Hadi.

The city has been the scene of some of the most intense fighting in a war that has pushed 14 million people to the edge of famine.

Intense talks, however, were continuing on Sanaa airport, shut down for years in the conflict between the Saudi-backed government and northern rebels linked to Iran.

Negotiators are also seeking a de-escalation of violence in rebel-held Hodeida, a port city vital to the supply of humanitarian aid, and a cooperation deal on the country's crumbling economy.

Hodeida, the lifeline to millions dependent on aid to survive, is home to major frontlines.

Another round of talks has been tentatively scheduled for January, according to UN and Yemeni officials.

The head of the Houthis' revolutionary council, Mohammed Ali Houthi, on Wednesday said the insurgents had proposed Yemen's rebel-held capital, Sanaa, to host the next round.

A UN official said the organization had received no such request.

UN Secretary-General Antonio Guterres was due at the talks in Rimbo, Sweden, for Thursday's closing round of consultations.

Agreement on port and airport

Ahead of the UN's chief's arrival, his office said it had evidence the rebel Houthis were using Iran-made missiles – a charge the Saudi-led alliance levels against the rebels as grounds for restrictions on the Hodeida port and Sanaa airport.

Both government and rebel representatives have traded accusations of unwillingness to negotiate, particularly on rebel-held Hodeida, the main route for 90 percent of food imports and nearly 80 percent of aid deliveries.

UN special envoy Martin Griffiths has submitted a proposal on a political framework for the future of Yemen, an agreement on the reopening of Sanaa airport, a paper on addressing the economic situation and a draft agreement on Hodeida, spokeswoman Hanan Badawi told reporters.

"The two parties have officially received the drafts and we are waiting on a response," Badawi said.

Members of both delegations told AFP agreements could be signed by morning.

Yemeni Prime Minister Moeen Abdulmalik Saeed said a full agreement on Hodeida was unlikely "given the time constraints."

Abdelmagid al-Hanash, of the Houthi delegation, told AFP an agreement on Sanaa airport was close, with the rebels open to a government proposal for flight searches in Sayoun or Aden, two cities under the control of the state.

"For now, the search will be in Aden but will not cause harm or trouble. No one will be asked to disembark," Hanash said.

An adviser to the government team, speaking on condition of anonymity, said his delegation would not confirm any agreement until the documents had been signed.

Yemeni ministers Othman Mujalli and Marwan Dammaj told reporters on Wednesday their camp would hold firm to UN Security Council Resolution 2216 – which calls for the Houthis to withdraw from all areas seized in a 2014 takeover, including Hodeida.

Representatives of both the Houthis and government blamed the other party for the lack of a truce on Hodeida.

The last official statement by a spokesman for the Saudi-led government coalition said military operations were ongoing in Hodeida on Monday night.

Saudi soldiers on missing list

Read also: Yemeni gov't, rebels swap names of 15,000 prisoners at UN talks

The two camps signed a mass prisoner exchange deal at the Sweden talks, which two Yemeni government officials confirmed include Saudi soldiers fighting alongside state troops. The Houthis had said Tuesday that the list included Saudi soldiers.

A spokesman for the Saudi-led coalition and a UN official did not immediately respond to a request for comment.

The prisoner swap includes the names of more than 15,000 detainees and disappeared persons taken on frontlines since 2015.

The deal will be overseen by the International Committee of the Red Cross, which warns the exchange could take weeks.

The Yemen conflict has killed nearly 10,000 people since the Saudi-led coalition joined the war in 2015, according to the World Health Organization, triggering what the UN calls the world's worst humanitarian crisis.

Both parties stand accused of failing to protect civilians. The Saudi-led alliance has been blacklisted by the UN for the killing and maiming of children.

(Cover: People watch a monument where the former head of the Houthi Supreme Political Council, Saleh al-Sammad, and his body guards are buried after their death during an April 2018 Saudi-led air strike, in Sanaa, Yemen, December 12, 2018. /VCG Photo)