The US is to end its support for offensive operations by its allies in Yemen, which has been devastated by a six-year war in which more than 110,000 people are believed to have died.
"The war in Yemen must end," President Joe Biden said in his first major foreign policy speech.
Under Mr Biden's two predecessors, the US backed a coalition led by Saudi Arabia against Houthi rebels in Yemen.
The conflict has left millions of Yemenis on the brink of starvation.
Fighting began in 2014 between a weak Yemeni government and the Houthi rebel movement. It escalated a year later, when Saudi Arabia and eight other Arab states - backed by the US, the UK and France - began air strikes against the Houthis.
Mr Biden announced other changes to US foreign policy, such as a significant increase in the number of refugees accepted by the US.
His speech marks a sharp break with the policies of former President Donald Trump, who left office last month.
On Russia, for instance, the new US leader said: "I made it clear to President [Vladimir] Putin, in a manner very different from my predecessor, that the days of the United States rolling over in the face of Russia's aggressive actions… are over."
The comments drew fierce criticism from the Kremlin. "This is very aggressive, unconstructive rhetoric, to our regret," Mr Putin's spokesman Dmitry Peskov said on Friday.
What does the Yemen announcement mean?
The US has been backing the Yemeni government and its Saudi-led allies in their war against the Houthis. As a result of Thursday's announcement, the US will stop supporting offensive operations, including the sale of precision-guided munitions to Saudi Arabia and the United Arab Emirates (UAE).
This will not affect operations against al-Qaeda in the Arabian Peninsula.
The Biden administration had already put a temporary halt on arms sales to Saudi Arabia and the UAE.
This marks a change of tack from Mr Trump's administration, which increased support for the Saudi-led coalition. Last month Mr Trump's Secretary of State, Mike Pompeo, announced that the Houthis were being designated a "terrorist organisation".
He said the aim was to hold the Houthis accountable for cross-border attacks and deter "malign activity" by their backer Iran.
Aid organisations criticised the move, warning that it could prevent them from operating in areas where millions are in urgent need of food aid.
Last week, the Biden administration said it would exempt certain transactions involving the Houthis from sanctions. That exemption will expire on 26 February.
The United Nations says Yemen is the world's worst humanitarian crisis, with 80% of the population in need of aid or protection.
These announcements confirm President Biden's pledge to end Yemen's destructive war. Halting US support to the Saudi-led coalition's offensive operations won't close this bloody chapter, but it sends a strong signal to leaders in Riyadh and Abu Dhabi - they've also been trying to find ways to extricate themselves from this quagmire.
Achieving peace among Yemen's bitter enemies will be a monumental challenge. Tim Lenderking is set to be the first US envoy for Yemen since this war was unleashed nearly six years ago. He's worked on this file for years and is known to everyone who matters.
Western diplomats, as well as Yemenis, have welcomed this new US engagement. In 2015, President Obama gave a green light to the Saudi-led campaign, partly to ease the Kingdom's anger over the Iran nuclear deal. Now new US envoys on Yemen, and Iran, are tasked with ending this war, and the regional rivalries which still fuel it.
What else did Biden say?
The US will raise the cap on refugee admissions from 15,000 to 125,000 for the fiscal year.
The withdrawal of US troops from Germany will be frozen and forces will remain at their current level of about 36,000. Under Mr Trump, the US was going to reduce its presence by 12,000, with about 5,600 to be deployed elsewhere in Europe.
Mr Biden called on Myanmar's military rulers to release civilian leader Aung San Suu Kyi and restore democracy.
He also promised to engage diplomatically with Russia but to be tougher on Moscow than Mr Trump, saying the US would not "roll over".