The United States has appeared to deepen its involvement in Yemen under the Donald Trump administration. In the fiscal year that ended in September, the Pentagon filled Saudi and Emirati jets bombing Iran-backed Houthi targets with 478,750 gallons of aviation fuel, costing taxpayers more than $1 million.

The defense secretary’s peace push comes as the Pentagon has engaged in a full-court press to stop US lawmakers from curtailing US support for the Saudi-led campaign. Mattis personally made an appearance at weekly Senate lunches on Capitol Hill this week to convince lawmakers of both parties to vote against a bipartisan bill to end US refueling and intelligence support for the war. The effort failed 55-44.

“We are going to end this war, that is the bottom line,” Mattis said at a joint ceremony before their meeting. “And we are going to end it on positive terms for the people of Yemen but also security for the nations in the peninsula.”

During a 45-minute meeting with visiting Crown Prince Mohammed bin Salman at the Pentagon, Mattis urged the Saudi leader to hasten peace talks that have taken on new life with last month's appointment of former British diplomat Martin Griffiths as the new UN envoy. Mattis called Riyadh “part of the solution” to the conflict Saudi Arabia entered in 2015, even as the mounting civilian death toll has stoked a backlash in Congress.

US Defense Secretary James Mattis today called on Saudi Arabia to “accelerate” the peace process in Yemen even as the Pentagon pushes to continue US refueling support for Riyadh’s bombing campaign against the Iranian-backed Houthi rebels.

Mattis’ push for a dedicated diplomatic effort comes after he returned last week from Oman, which has forged a back channel between Saudi Arabia and the Iran-backed Houthis to try to end the conflict. Oman’s ailing Sultan Qaboos bin Said has long provided American diplomats with an avenue for talks with Iran dating to the 1979 US hostage crisis, and could provide a crucial conduit for negotiations between Riyadh and the Houthis.

“There is a window of opportunity to get something going on the political front,” said Gerald Feierstein, a former US ambassador to Yemen. “The Omanis seem to be trying to get engaged in pushing for a return to negotiation. There are reports that the Saudis and the Houthis have begun talking.”

Progress on the diplomatic front could notably help facilitate pending US arms sales to Riyadh, which Trump emphasized during his meeting with Prince Mohammed at the White House on Tuesday with a posterboard advertising the $110 billion weapons deal advanced last year, most of which was first negotiated under the Barack Obama administration. Congress has repeatedly tried – and failed – to block Saudi arms sales, citing the carnage in Yemen, causing delays and public relations headaches in both Washington and Riyadh.

The crown prince visited the CEO of Lockheed Martin in Washington this week, and will head to the company’s Sunnyvale, Calif., facility during the second leg of his trip. That’s where the missile-defense system Terminal High Altitude Aerial Defense (THAAD), which the Trump administration agreed to sell to the Saudis for $15 billion last fall, is produced.

The State Department also approved significant arms deals on the last day of Mohammed's Washington visit Thursday, notifying Congress of $1 billion in potential sales to provide Saudi Arabia with nearly 6,700 tube-launched missiles, repairs for Abrams tanks, Humvees, and Bradley Armored Fighting Vehicles, and US-made Apache and Bell helicopters that Riyadh has used throughout the military campaign in Yemen. The Saudi National Guard deployed an American-trained helicopter unit to the fractious border with Yemen in October and is training three aviation brigades.

Even as they discuss peace in Yemen, the Saudis are pressing the United States take a more aggressive posture against Iran as Mohammed takes the reins. A Saudi government-made video that racked up more than a million hits on YouTube after it went online in December showed the crown prince staging an ambitious invasion of Iran that culminated in Iranians cheering the heir to the throne in the streets.

“The Emirates and the Saudis would like to see a greater confrontation with Iran,” Feierstein, now director for Gulf affairs at the Middle East Institute, told Al-Monitor. “They’re going to be the ones with the big bullseye on them, not the US.”

With Iran’s presence in Yemen and the nearby Bab el-Mandeb Strait deeply entrenched after years of war, a diplomatic solution remains a long shot. Speaking to reporters on a flight back from the Middle East last week, Mattis called the strait “the Aberdeen Proving Ground,” referring to a US military weapons test site established during World War I. Tehran has reportedly launched tests of its ballistic and cruise missiles in the strait that separates Yemen and Africa; mines and explosive boats believed to have been provided by Iran are also threats there.

Both the Pentagon and US allies in the Gulf, including Saudi Arabia and the United Arab Emirates, hope to stop Iran from developing the strait into a transshipment point for weapons supplies to the Houthis in Yemen. In 2016, US, French and British warships interdicted thousands of assault rifles and anti-tank weapons headed for Yemen and Somalia.

“It is difficult to identify a strategic driver for the US to withdraw its non-lethal support,” said Norman Roule, a former CIA officer who served as national intelligence manager for Iran from 2008 until 2017. He said the Saudis and the international community "can’t tolerate an adversary such as Iran’s Revolutionary Guards in Yemen or operating surrogates on the Bab el-Mandeb. For this reason, a political solution won’t be acceptable if it doesn’t mean an end to Iran’s presence in Yemen.”