U.S. Secretary of State Marco Rubio reaffirmed Washington's commitment to the North Atlantic Treaty Organization (NATO) during his first meeting with the alliance's foreign ministers, while emphasizing the need for more defense spending in Europe.

"President Trump has made it clear he supports NATO. We are going to remain in NATO," Rubio told reporters Thursday in Brussels. "The only way NATO can get stronger and more viable is if our partners - the nation-states that comprise this important alliance - have more capability."

Rubio said he hoped to leave the meeting with a clear pledge from allies to raise defense spending to 5 percent of their gross domestic product. That figure would more than double NATO's current target of 2 percent, a benchmark some member states have yet to meet.

Rubio acknowledged that the proposed 5 percent goal could not be achieved "in one year or two," but said that the U.S. now demanded a real path forward from its allies to build a stronger NATO capable of defending its territories.

NATO Secretary General Mark Rutte noted that Europe and Canada have made the largest defense spending increases since the Cold War, but echoed Rubio's call for further efforts.

Speaking on his way to the meeting, Rutte said he believed defense spendings by European and Canadian allies would need to exceed 3 percent of GDP to meet future security challenges.