BRUSSELS — NATO foreign ministers on Tuesday reaffirmed their commitment to defend each other against outside attack and underlined the strength of relations between North America and Europe, after four years of doubt and concern among some allies under the Trump administration.

"We are now opening a new chapter in our trans-Atlantic relationship," NATO-Secretary General Jens Stoltenberg told reporters after chairing the talks. He thanked President Joe Biden for committing "to rebuild the strength of this alliance" and make it "future-proof in a more competitive world."

In a formal joint statement aimed at turning a page on the Trump era, the ministers said: "We are meeting in Brussels to reaffirm the enduring transatlantic bond between Europe and North America, with NATO at its heart."

The ministers, including U.S. Secretary of State Antony Blinken, also committed to the collective defense clause — Article 5 of NATO's founding treaty — under which an attack against one ally shall be considered an attack against them all. It has only been activated once by NATO, after the 9/11 attacks on New York and Washington.

Former U.S. President Donald Trump often criticized NATO partners for failing to pay their defense dues, claiming falsely that they owed the alliance or the United States money. 

Early in his tenure, he threatened not to come to the defense of any country that did not meet NATO spending guidelines, causing deep concern among member nations close to Russia's borders, like Estonia, Latvia, Lithuania and Poland.

The ministers noted that members of the 30-nation alliance "are making good progress on fairer trans-Atlantic burden sharing; we welcome the efforts made by all Allies in Europe and North America that contribute to our indivisible security. We must and will do more."

They also vowed that NATO would continue to adapt in the face of "rising threats and systemic competition," and underlined that "Russia's aggressive actions constitute a threat to Euro-Atlantic security."

Earlier, Blinken said that the U.S. is "determined to revitalize our alliances, to revitalize our partnerships, starting with NATO."

"When we look at virtually all of the challenges that we face as a country and that are actually going to potentially affect the lives of our citizens, not a single one of them can be effectively dealt with by any one country acting alone, even the United States with all of the resources that we have," he said.

The U.S. is by far the biggest and most influential member of NATO, and Trump also surprised, confounded and sometimes angered allies with unilateral decisions, like pulling U.S. troops out of Afghanistan and northern Syria. France complained about a lack of U.S. leadership at NATO.

Asked about NATO member Turkey, Stoltenberg acknowledged that the allies have differences over Ankara's decision to buy Russian anti-aircraft missiles or its aggressive behavior in the eastern Mediterranean Sea, notably a standoff over energy exploration with Greece and Cyprus.

"We need to use NATO as a platform and consult when there are differences," he said, expressing hope that a series of proposals he has drafted to address problems within the alliance will be endorsed by Biden and fellow NATO leaders when they meet in Brussels in June.