The US has called for a swift cessation of hostilities in Yemen, where three years of civil war have caused the world’s worst humanitarian crisis.
Defence Secretary James Mattis said all parties needed to take part in UN-led peace talks within the next 30 days.
Secretary of State Mike Pompeo meanwhile urged the Saudi-led coalition battling the rebel Houthi movement to end its air strikes on populated areas.
The US has faced growing pressure to end its support for the coalition.
UN human rights experts say coalition forces may have committed war crimes in Yemen and humanitarian organisations say their partial blockade of the country has helped push 14 million people to the brink of famine.
The murder of the US-based journalist Jamal Khashoggi by Saudi agents in Istanbul this month has also strained ties between Washington and Riyadh.
Yemen has been devastated by a conflict that escalated in early 2015, when the Houthis seized control of much of the west of the country and forced President Abdrabbuh Mansour Hadi to flee abroad.
Alarmed by the rise of a group they saw as an Iranian proxy, the UAE, Saudi Arabia and seven other Arab states intervened in an attempt to restore the government. They have received logistical and intelligence support from the US, UK and France
Speaking at the US Institute of Peace in Washington on Tuesday, Mr Mattis said the US had been watching the conflict “for long enough”.
“We have got to move towards a peace effort here, and we can’t say we are going to do it sometime in the future. We need to be doing this in the next 30 days,” he said.
Mr Mattis added that all sides were being urged to meet UN special envoy Martin Griffiths in Sweden in November and “come to a solution”.
In a separate statement, Mr Pompeo called on the Houthis to end missile and drone strikes on Saudi Arabia and the UAE, and on the coalition to cease air strikes on all populated areas in Yemen.
“It is time to end this conflict, replace conflict with compromise, and allow the Yemeni people to heal through peace and reconstruction,” he added.
The Trump administration has previously backed Mr Griffiths’ mediation efforts and called for a political solution to the conflict in keeping with UN Security Council 2216, which demands that the Houthis withdraw from all areas they have seized and to relinquish their heavy weapons. The Houthis have rejected the resolution.
For months the Trump administration has said little about this bloody conflict, leaving its Saudi allies to take the lead. But the remarks by Mr Mattis and Mr Pompeo show the US is now engaging in a way it has not for some time.
Until now both the US and the UK have resisted calling formally for a ceasefire through the UN while it was obvious that neither side was willing to contemplate one. But that seems to have changed. The question, of course, is why?
Diplomats point to the growing pressure from the US Congress to act ahead of the mid-term elections. The US might also be hoping to use the backlash against Saudi Arabia over the murder of Jamal Khashoggi to put pressure on Riyadh to try to end the conflict. Some diplomats have even spoken of a Saudi compromise on Yemen being part of the rehabilitation of Crown Prince Mohammed Bin Salman, the kingdom’s de facto leader.
The big question is how Iran will react. Some diplomats have suggested that Tehran would not be unhappy to step back from Yemen, that its involvement there was always opportunistic rather than strategic, and that it has bigger priorities elsewhere. But it is not clear whether Iran would be willing to help the US when it is re-imposing sanctions on its economy after withdrawing from the Iran nuclear deal.
So the US move is important, but there is still a long way to go before a ceasefire becomes possible, let alone a political process to end the conflict for good.
There was no immediate response from the Saudi-led coalition, the Houthis or Yemen’s government.
Mr Griffiths said the UN welcomed the calls for a cessation of hostilities and stressed that there could be no military solution to the conflict.
“We remain committed to bring the Yemeni parties to the negotiations table within a month. Dialogue remains the only path to reach an inclusive agreement,” he said.
UK Foreign Secretary, Jeremy Hunt, tweeted: “All parties must listen to the important call from the US for de-escalation in Yemen, in line with the UK’s long-standing position. I discussed this issue with Martin Griffiths… at the FCO last night and we must back his efforts to find a political solution to the hilt.”
A spokeswoman for the International Rescue Committee, a charity operating in Yemen, said a ceasefire and peace talks needed to happen as soon as possible so aid could be delivered to those suffering the most.
“From our perspective there’s a lot that could have been done before a call for this ceasefire, but the ceasefire is a significant breakthrough in this war and a welcome recognition that the current policy is failing,” Kellie Ryan said.