Defense Secretary Jim Mattis gave a full-throated defense Friday of U.S. efforts to prevent civilian casualties in the conflict in Yemen, making the case that without American involvement, there would be more.

Mattis, speaking to reporters at the Pentagon, said that “it’s a tragedy every time” a civilian dies, but that the United States is held to a high standard when it comes to preventing civilian fatalities.

“We are being held to a standard – ‘we’ being us and anyone associated with us – that has never been achieved before in warfare,” he said.

The comments came after two separate airstrikes on Dec. 26 by a Saudi-led coalition fighting Houthi rebels in Yemen killed dozens of people and prompted a rebuke from a top United Nations official in the country. Initial U.N. reports said that at least 54 civilians, including eight children, were killed in a strike on a crowded market, and an additional 14 people from one family were killed in a bombing on a farm.

The United States does not drop bombs as a part of the Saudi-led air war against the Houthis, but provides aerial refueling to Saudi jets, shares intelligence to improve their targeting and attempts to teach Saudi pilots how to be more accurate. Mattis bristled Friday when a reporter suggested that the effort isn’t working, saying “that’s your call.”

Asked whether he was “okay” with the current level of civilian casualties, the defense secretary grew stern.

“I’m never okay with any civilian casualty,” he said. “Don’t screw with me on this.”

The U.S. military’s handling of civilian casualties has remained in question in several war zones in which the U.S. military operates, especially as it touts the campaign against the Islamic State in Iraq and Syria as the most precise in world history. An extensive New York Times investigation published in November found that about 1 in 5 airstrikes in a sampling of 150 bombing sites surveyed by the Times resulted in a civilian death, with many uncounted by the coalition.

Mattis said that in Yemen, the Saudi government is attacking Houthi rebels “with military necessity in their minds.” The rebels have launched numerous ballistic missiles over the Yemeni border into Saudi Arabia.

The United States targets Al-Qaeda in the Arabian Peninsula (AQAP) militants in Yemen, but has mostly avoided targeting the Houthis themselves. One exception occurred in October 2016, when the Navy launched “limited self-defense strikes” using Tomahawk missiles at rebel radar sites after several missiles were launched at Navy ships.

The war between the Saudis and Houthis dates back to March 2015, when the Saudis intervened on behalf of Yemeni President Abed Rabbo Mansour Hadi after the Houthis attempted to overthrow him.

Mattis said the U.S. military will continue to work with Saudi pilots to improve their bombing and target identification. He noted that other military forces that are part of the North Atlantic Treaty Organization (NATO) required U.S. assistance as they struggled to prevent civilian casualties in their operations in Libya after the 2011 U.S.-led intervention there.

“Not all nations can be held to the standard that we’ve achieved,” Mattis said.

Mattis visited the press center in the Pentagon to wish journalists a Happy New Year, and unexpectedly went on the record in a wide-ranging conversation that lasted about 45 minutes.

The defense secretary said he expects more U.S. civilians involved in the reconstruction effort in Syria in 2018, including contractors and “more diplomats.” The effort, he said, will be geared toward stabilizing the country, with the U.S. military in a support role to provide security and transportation.

“It is an attempt to move toward the normalcy and that takes a lot of support,” Mattis said.

Mattis also predicted that more conventional U.S. troops will take on missions that were once the province of Special Operations forces in 2018 — an effort to reduce deployments of the Pentagon’s most elite forces after years of heavy use.

“If I was to put it in philosophical terms, you want a force that can deal with today’s challenges and not be dominant in yesterday’s challenges,” Mattis said. “The general-purpose forces are going to have to have some of the capabilities that you and I used to only associate with Special Forces.”

He added that over time, capabilities once associated with Special Operations troops have transitioned to being conventional military missions. In one example, a new Army Security Force Assistance Advisory Brigade is expected to deploy in the spring, training Afghan forces as part of an increase in U.S. troop deployments approved by President Trump.

Mattis declined to offer any message to transgender people who might seek to enlist in the military beginning Jan. 1, when a federal court has ordered the Pentagon to allow them to do so. That came in response to legal challenges to President Trump’s proposed ban on all transgender people serving.

“I’m not going to get into this right now,” Mattis said. “It’s a court case right now. The Department of Justice is handling it. If they’re not appealing it, we’ll be notified of that. And I don’t get into singling out and welcoming this group or that group or that gender or anything else. That’s not my role.”

Asked how he feels about his first year as defense secretary, Mattis played it coy.

“I don’t have any feelings,” he said, deadpan.

As to whether he planned to stay in office through Trump’s term, he replied: “I take one day at a time.”