Vice President Mike Pence has announced plans for a new, separate U.S. Space Force as sixth military service by 2020.

Pence says it's needed to ensure America's dominance in space amid heightened completion and threats from China and Russia. He says that while space was once peaceful and uncontested, it is now crowded and adversarial.

President Donald Trump has called for a "separate but equal" space force. Defense Secretary Jim Mattis has endorsed plans to reorganize the military's space warfighting forces and create a new command, but has previously opposed launching an expensive separate new service.

Any proposal to create a new service would require congressional action.

Trump officially directed the Department of Defense to establish a sixth branch of the U.S. military in space back in June, saying the space force would ensure American dominance in the final frontier. 

"It is not enough to merely have an American presence in space. We must have American dominance in space," Trump said. Pence tweeted ahead of his remarks that "space is 'a war-fighting domain, just like the land, air, and sea.'"

The space force intends to organize, train, and equip people in the interest of space-related national security. It could, eventually, lead missions to other planets, including Mars.

Pence currently serves as chair for the president's revitalized National Space Council. 

(The Associated Press, CBS News contributed to this report.)