U.S. President Donald Trump instructed the National Aeronautics and Space Administration on Monday to send astronauts back to the moon in an effort to lay a foundation for a mission to Mars.

In signing the directive, Trump said the move "marks an important step in returning American astronauts to the moon for the first time since 1972 for long-term exploration and use."

Trump said the directive will reassert U.S. leadership in space and refocus America's space program on human exploration and discovery.

(NASA)

"This time, we will not only plant our flag and leave our footprint, we will establish a foundation for an eventual mission to Mars," he said during a signing ceremony at the White House. "And perhaps, some day, to many worlds beyond."

The president, however, did not touch on specifics such as when and for how long astronauts will explore the moon and how the U.S. government will finance the project.

Under a NASA plan, the United States will carry out a landing to the moon in partnership with other countries and the U.S. private sector, leading Japan to consider extending cooperation.

The United States is expected to present the project during the International Space Exploration Forum that Japan will host in March in Tokyo.

At Monday's ceremony, Trump was joined by current and retired astronauts including Apollo 17 astronaut Harrison "Jack" Schmitt, one of the last Americans to land on the moon in December 1972.

"Today, we pledge that he will not be the last," Trump said of Schmitt. "And I suspect we'll be finding other places to land in addition to the moon."

Trump said that space has much "to do with so many other applications," including in the military field.

In a separate address, Vice President Mike Pence said that "the rules and values of space exploration are written with American leadership and American values," a message apparently directed to countries such as Russia and China.