Foreign ministers from NATO's 29 member countries are scheduled to open a two-day meeting in Washington on April 3 to honor the alliance's 70th anniversary and discuss security threats, including Russia and Afghanistan.
Ahead of the gathering, U.S. President Donald Trump met NATO chief Jens Stoltenberg at the White House on April 2 and pressed his demands that the allies do more to pay for their own defense.
Stoltenberg is scheduled to address Congress on April 3, the first NATO secretary-general to do so.
NATO foreign ministers are due to attend a reception at the Andrew W. Mellon Auditorium, where President Harry S. Truman hosted the original 12 member nations that signed the accord establishing the North Atlantic Treaty Organization in 1949.
On April 4, the foreign ministers will hold meetings at the State Department, with a first session focusing on Russia.
They are expected to endorse a set of measures in the Black Sea to improve NATO's defenses in the region.
The situation in Afghanistan as well as the demise of a landmark arms-control treaty that the United States and Russia signed in the last years of the Cold War, and NATO member Turkey's decision to buy a Russian surface-to-air missile system, will also be on the agenda.
The Russian system is not compatible with NATO systems and is considered a threat to U.S. F-35 aircraft.
On April 2, Trump praised member countries for increasing their financial contributions to NATO, but said the United States still shoulders a disproportionate share of the cost of protecting Europe.
"We are protecting countries that have taken advantage of the United States," Trump said. "The United States pays for a disproportionate share of NATO," Trump said, adding: "We just want fairness."
Trump has called on NATO allies to increase their defense spending to the agreed level of 2 percent of gross domestic product (GDP) and even much higher. He said during his meeting with Stoltenberg that most nations are missing the target, although he cited progress.
Stoltenberg thanked Trump for his "strong commitment to NATO" and for his leadership in getting member nations to increase their commitments.
Spending by the 29 NATO countries, which dropped after the end of the Cold War, has actually been on the rise since 2014 -- before Trump took office.
After Russia annexed Ukraine's Crimean Peninsula in 2014, allies agreed to boost defense spending and "move toward" spending 2 percent of their GDP on defense by 2024. The U.S. spends 3.4 percent of its GDP on defense.
Trump singled out Germany, which recently announced plans to increase defense spending to 1.25 percent of its GDP by 2023 -- a revision of Chancellor Angela Merkel's pledge last year to hit 1.5 percent by 2024.
"Germany honestly is not paying their fair share," the U.S. president said, sitting next to Stoltenberg.
Trump has at times voiced doubts about NATO, in particular Article 5, its mutual defense clause, which stipulates that an attack against one NATO ally will be regarded as an attack against all.
With reporting by AP, AFP, and dpa