President Donald Trump said Friday that he will defer to the judgment of Defense Secretary James Mattis that torture and waterboarding should continue to be banned in the interrogations of terror suspects.

"He has stated publicly that he does not necessarily believe in torture or waterboarding or however you want to define it," Trump said of Mattis, a retired Marine general who had commands in Iraq and Afghanistan. "I don't necessarily agree, but he [Mattis] will override because I'm giving him that power."

"I'm going to rely on him" on so-called "enhanced interrogation techniques," Trump said, though "I happen to believe it does work."

Trump said Mattis told him in December that he could get more out of a terror suspect with "a pack of cigarettes and a beer" than he could with torture.

At a White House news conference with British Prime Minister Theresa May, Trump also said that the subject of lifting sanctions on Russia might come up in his phone call Saturday with Russian President Vladimir Putin.

"I hope we have a fantastic relationship," Trump said of closer cooperation with Russia on a range of issues. "It's also possible that we won't. If we could have a great relationship with Russia, with China and all countries -- I'm all for that."

As she stood next to Trump, May made clear that she disagreed with him on the sanctions. "We believe sanctions should continue, and we have continued to urge that inside the European Union."

Earlier, Kellyanne Conway, Trump's counselor, said on "Fox and Friends" that lifting sanctions and the possibility of cooperation between the U.S. and Russia in the war against the Islamic State of Iraq and Syria were likely topics of the Trump-Putin phone call. "All of that is under consideration," she said.

Sen. John McCain, an Arizona Republican and chairman of the Senate Armed Services Committee, issued a statement calling on Trump to keep the sanctions in place and threatening moves to put the sanctions into law if the president lifts them.

"In just the last three years under Vladimir Putin, Russia has invaded Ukraine, annexed Crimea, threatened NATO allies, and intervened militarily in Syria, leaving a trail of death, destruction, and broken promises in his wake," McCain said.

"Trump should remember that the man on the other end of the line is a murderer and a thug who seeks to undermine American national security interests at every turn. For our Commander-in-Chief to think otherwise would be naïve and dangerous," McCain said.

Following the news conference, Trump was headed for the first time to the Pentagon for meetings with Mattis and the Joint Chiefs of Staff to discuss a more aggressive ISIS campaign and his pledge to rebuild the military with more troops, ships, planes and money.

Trump was to meet with the nation's military leadership in the "Tank," the Joint Chiefs of Staff conference room, and later preside at a ceremonial swearing in of Mattis, the 26th secretary of defense.

Mattis took the oath last Friday night from Vice President Mike Pence in the old Executive Office Building next to the White House, but the ceremonial swearing in held at the Pentagon's Hall of Heroes, a room dedicated to the more than 3,400 recipients of the Medal of Honor, is traditional for defense secretaries. Pence was to join the Pentagon meetings after attending an anti-abortion "March For Life" rally Friday morning that was to end at the Supreme Court.

Syria's more than five-year-old civil war and the offensive by the U.S.-backed Syrian Democratic Forces on Raqqa, the self-proclaimed ISIS capital, were expected to be at or near the top of the agenda for Trump's talks with Mattis and the service chiefs.

Mattis in his Senate confirmation hearings spoke of the possibility of an "accelerated" campaign against ISIS in Iraq and Syria. The U.S. ground commander for Iraq said earlier this week that he had received no notice of plans to change troop levels or rules of engagement since Trump took office.

In a briefing to the Pentagon, Army Maj. Gen. Joseph Martin, commander of Combined Joint Forces Land Component Command-Operation Inherent Resolve, said, "Our orders have not changed since the 20th of January" when Trump was inaugurated.

"I can't speculate on what the future's going to hold," Martin said, but his troops were still operating under the orders approved by former President Barack Obama.

Trump is expected to ask Mattis and Secretary of State nominee Rex Tillerson for a new plan within 30 days to speed up the ISIS campaign.

Trump and Pence were greeted by Mattis as they arrived at the Pentagon at about 3:30 p.m. and then went into about an hour-long closed meeting with Joint Chiefs Chairman Gen. Joseph Dunford; Air Force Gen. Paul Selva, the vice chairman of the Joint Chiefs; and the service chiefs.

Retired Army Lt. Gen. Michael Flynn, the new White House national security adviser, also was in the closed meeting, a Pentagon spokesman said. White House strategist Steve Bannon was at the ceremonial swearing-in, but it was unclear if he was also in the meeting with the Joint Chiefs, Trump and Mattis.

At the ceremony in the Hall of Heroes, Trump dropped his usual reference to Mattis with the nickname he doesn't like -- "Mad Dog" -- and instead called him a "man of total action; he likes action."

Pence administered the ceremonial oath of office, as he had last week at the official swearing in of the Marine Corps legend. Pence noted the names of 3,498 recipients of the Medal of Honor that are inscribed on the walls of the Hall of Heroes.

"It is humbling for us to be among their names," he said.

In his last post as head of U.S. Central Command before retiring in 2013, Mattis had charge of about 200,000 personnel. Pence said, "Mr. Secretary, your president has called you to lead all of the armed forces of the United States."

In brief remarks, Mattis told Trump and Pence: "Welcome to the headquarters of your military, your always loyal military, where America's awesome determination to defend herself is on full display.

"I'll just tell you, Mr. President, you've made clear your commitment to our national defense, and the Americans in this hall [the lists of Medal of Honor recipients] remind us of our strength as a nation of patriots," he said.

"On behalf of your department, I want you to know that after a decade of war, our longest war, those serving today have been tested and you can count on us all the way," Mattis said.

Trump used the occasion to sign what he called two "executive actions" signaling his intent to boost military spending and troop strength, and to impose "extreme vetting" on those entering the country.

He gave no details but promised a "great rebuilding of the armed services of the United States" that will involve "developing a plan for new planes, new ships, new resources and new tools for our men and women in uniform, and I'm very proud to be doing that."

"As we prepare our budget request for Congress, and I think Congress will be very happy to see it, our military strength will be questioned by no one, but neither will our dedication to peace. We do want peace," Trump said.

The extreme vetting is needed to "keep radical Islamic terrorists out of the United States of America. We don't want them here," he said. "We want to ensure that we are not admitting into our country the very threats our soldiers are fighting overseas. We only want to admit those into our country who will support our country and love, deeply, our people."

Trump promised the audience of Pentagon staffers and uniformed personnel, "Our administration will always have your back; we will always be with you."

He said of Mattis, "I think he's going to lead us so brilliantly. He's a tremendous soldier, always has been. He's a general's general. He's a special, special man."

-- Richard Sisk can be reached at Richard.Sisk@Military.com.