U.S. astronaut Peggy Whitson, member of the 50/51 expedition to the International Space Station (ISS).

President Donald Trump called the International Space Station on Monday to congratulate astronaut Peggy Whitson for staying in space longer than any other American.

Whitson, who has been at the ISS for 534 days and counting, is scheduled to stay there for at least another five months.

Her record surpasses that of fellow American astronaut Jeff Williams.

"That is an incredible record to break, and on behalf of our nation," Trump said during a call to the ISS on Monday morning, "and frankly on behalf of the world, I would like to congratulate you."

Whitson, 57, also holds the record for being the oldest American woman in space, and the first woman to command the ISS twice.