President Donald Trump said Tuesday the U.S. and Saudi Arabia have entered into a security agreement that will ease weapons transfers and elevate the relationship between the two countries.

Under the agreement, Saudi Arabia would be designated a “major non-NATO ally,” a formal relationship that deepens defense cooperation but does not include a security guarantee. The Kingdom would join 19 other countries in that category, a list that includes Israel, Jordan, Kuwait and Qatar.

Saudi Arabia has long been an important Middle East ally of the U.S. but relations have been strained at times over human rights, oil policy and Israel, among other issues. Trump has long made relations with the Kingdom a priority, visiting the country on his first overseas trips in both his first and second terms.

“A stronger and more capable alliance will advance the interests of both countries, and it will serve the highest interest of peace,” Trump said at a black-tie dinner at the White House with Crown Prince Mohammed bin Salman, Saudi Arabia’s de-facto leader.

The announcement followed the crown prince’s announcement that he would increase his nation’s investments in the U.S. from about $600 billion to nearly $1 trillion — and after Trump dismissed a question about the 2018 killing of a Washington Post columnist in which Mohammed was implicated by the CIA.

“Today is a special day,” the crown prince said at the dinner. “We think the horizon of the economic cooperation between Saudi Arabia and America is bigger and wider in many areas. We’ve been signing a lot of agreements that can open the door to develop the [relationship] deeper in many areas.”

In addition to easing weapons transfers, the agreement will open Saudi Arabia as a location to store U.S. weapons, and make the country eligible to bid on Pentagon maintenance and repair contracts and purchase depleted uranium ammunition.

The U.S. is not treaty-bound to come to the country’s defense as it would be with NATO allies.