President Donald Trump announced Monday he is directing the Pentagon to create a new "Space Force" as an independent military service branch aimed at ensuring American supremacy in space — though he may have limited power to develop a new military command.

While Trump has previously talked about his desire for a space unit, he seemed to take those musings one step further, specifically ordering the Pentagon to begin the creation of a sixth branch of the American armed forces.

"When it comes to defending America, it is not enough to merely have an American presence in space. We must have American dominance in space," Trump said during remarks at the White House. "We are going to have the Air Force and we are going to have the Space Force, separate but equal."

Turning to seek out Marine Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, Trump said, "General Dunford, if you would carry that assignment out, I would be very greatly honored also ...Where's General Dunford? General? Got it?"

Dunford appeared to acknowledge the order, responding, "we got it." But the directive seemed to take defense officials by surprise. Creating a new joint military command is largely the purview of Congress, which would have to provide the authority and any funding or shifting of money to a new unit.

Pentagon spokeswoman Dana White said that the department understands the president's guidance, and is working on the matter while taking into consideration the implications for intelligence operations for the other services. "Working with Congress, this will be a deliberate process with a great deal of input from multiple stakeholders," she said.

A senior congressional aide said that Trump's order is consistent with efforts by members of Congress over the past two years to find a way to dedicate additional resources to the country's warfighting in space. But the issue has been contested, and even Defense Secretary Jim Mattis expressed some early reluctance to creating a new military service citing the expense and broader effort to integrate warfighting.

The Defense Department is already in the middle of a congressionally-mandated review of the space force issue. The study began in March, with an interim review due in August and a final report due December 31. It's not clear if the president's comments Monday were meant to override or influence that study.

Decades ago, the military deemed space a critical war-fighting domain, creating the Colorado-based Air Force Space Command in 1982. It includes more than 36,000 personnel around the world that provide space and cyber capabilities for the Defense Department. And the Space and Missile Systems Center at Los Angeles Air Force Base in California, designs and buys most of the Pentagon's space systems, while also overseeing satellite and other aircraft launches.

In addition, a number of federal defense agencies control portions of the space program, including NASA and the National Reconnaissance Office, which develops and operates surveillance spacecraft and satellites for intelligence gathering.

In a March document outlining the review, the Pentagon said it has already made organizational changes to beef up the stature of the space force, but is reviewing others. The document sent to Congress said the review will look at research, capabilities, acquisition and joint warfighting needs, and will assess "whether the Space Corps concept should be implemented."

The establishment of an independent space force was mentioned by Trump in a March speech to service members in California, but it has faced opposition since it could create an expensive new headquarters bureaucracy and trigger complex and divisive battles between the agencies that currently control part of the space mission. So far, the Pentagon doesn't have any cost estimates for the development of a new command, or any description of how it would be set up or its impact on other defense and intelligence agencies.

Ever since the Space Age started with the Soviet Union's launch of Sputnik, there has been a military and national security aspect to space, even though there are treaties and a United Nations committee that explicitly talk about keeping space a place of peace. In the 1950s, President Dwight Eisenhower established two separate space programs — a civilian one that became NASA, and a military one.

Trump more broadly envisioned a bright future for the U.S. space program, pledging to revive the country's flagging efforts, return to the moon and eventually send a human mission that would reach Mars. The president framed space as a national security issue, saying he does not want "China and Russia and other countries leading us." While the U.S. has dominated in space since the 1969 moon landing, China is making strong headway, while Russia is in decline.

"My administration is reclaiming America's heritage as the world's greatest spacefaring nation," Trump said in the East Room, joined by members of his space council. "The essence of the American character is to explore new horizons and to tame new frontiers."

The president also used the White House event to establish a new policy for reducing satellite clutter in space. The policy calls for providing a safe and secure environment up in orbit, as satellite traffic increases. It also sets up new guidelines for satellite design and operation, to avoid collisions and spacecraft breakups.

The council's executive secretary, Scott Pace, told reporters before the meeting that space is becoming increasingly congested and current guidelines are inadequate to address the challenge.

Trump also encouraged SpaceX, Blue Origin and other nontraditional aerospace companies led by wealthy U.S. entrepreneurs to beat NASA to Mars.

"Just go ahead, if you beat us to Mars, we'll be very happy, and you'll be even more famous," he said. "As long as it's an American rich person, that's good, OK? They can beat us. We'll save a little money, and they can beat us, and we're taking full credit for it, don't worry about it."