Riyadh, Washington must pursue 'urgent efforts' for Yemen peace
The pair met at the Pentagon as part of Prince Mohammed's tour of the United States, which kicked off this week with a White House visit.
"As you discussed with President (Donald) Trump on Tuesday, we must also reinvigorate urgent efforts to seek a peaceful resolution to the civil war in Yemen and we support you in this regard," Mattis told Prince Mohammed.
Mattis said he believes Saudi Arabia is "part of the solution".
"They have stood by the United Nations-recognised government and we are going to end this war, that is the bottom line. And we are going to end it on positive terms for the people of Yemen, but also security for the nations in the peninsula," Mattis added.
Saudi Arabia leads a coalition in Yemen fighting the Houthi rebels.
The devastating three-year-old conflict was an early proving ground for the prince but it has been beset by allegations of atrocities against civilians, and strategic drift.
Just hours after the prince left the White House on Tuesday, the US Senate rejected a bipartisan bid designed to curtail US support for the war, which includes air-to-air refuelling of Saudi jets as well as target and intelligence sharing.
MbS, who also serves as the kingdom's defence minister, spearheaded the war on Yemen's Houthis in 2015, bringing together a Saudi-led coalition to intervene in the neighbouring country.
The US has provided weapons, intelligence and aerial refuelling to the coalition supporting Yemen's government against Iran-backed rebels.
Some US lawmakers have long expressed concern about the conflict, where civilian casualties from coalition airstrikes have drawn criticism from rights groups.
But last week, Mattis asked Congress not to interfere with America's role in the war, warning that restrictions could increase civilian casualties, jeopardise counterterrorism cooperation, and "reduce our influence with the Saudis".
More than 10,000 people have been killed and tens of thousands wounded in Yemen's three-year-old war, which is seen as both a civil conflict and a proxy war between regional titans Saudi Arabia and Iran.
The United Nations has described it as the world's largest humanitarian disaster.
On the eve of MbS' meeting with President Donald Trump, Saudi Foreign Minister Adel al-Jubeir justified the deadly war on the Middle East's poorest country by comparing to a Mexican threat to America.
"What would you do if militias tried to take over Mexico and started lobbing missiles at you? Sit there and take it?" Jubeir told journalists in Washington.