President Donald Trump insisted on his support for the NATO alliance Tuesday but again insisted that members must pay their way and warned it is not his job to "represent the world."

The new leader spooked allied capitals during his campaign by arguing that US support for NATO should depend on members increasing defense spending, but has since been at pains to defend the pact.

"My job is not to represent the world. My job is to represent the United States of America," he told US lawmakers in his maiden address to both houses of Congress, 40 days after taking office.

"We strongly support NATO," he said. "But our partners must meet their financial obligations.

"We expect our partners, whether in NATO, in the Middle East or the Pacific to take a direct and meaningful role in both strategic and military operations, and pay their fair share of the cost."

"And now, based on our very strong and frank discussions, they are beginning to do just that."

"In fact, I can tell you the money is pouring in," Trump added in a departure from his prepared remarks.