Vice President Pence called Thursday for America to assert its dominance in space as he made a direct appeal to the Pentagon for a sixth military branch serving this purpose -- and revealed the Trump administration wants to create the “Space Force” by 2020.

In a speech to the Defense Department, he said that countries such as Russia, China, North Korea and Iran are pursuing ways to “bring new weapons of war into space itself.”

“As their actions make clear, our adversaries have transformed space into a warfighting domain already and the United States will not shrink from this challenge,” he said. “Under President Trump’s leadership, we will meet it head on -- to defend our nation, and build a peaceful future here on Earth and in space.”

Trump said last week that he had ordered the Pentagon to begin the process of creating a Space Force as a new branch of the military.

Pence said on Thursday that it was an idea “whose time had come” and made clear that the White House wants to get on with the project as soon as possible. He hailed a new report by the Pentagon on the force as a starting point.

“President Trump and I are grateful to Secretary Mattis for this department’s diligence in preparing this report, and our administration will soon take action to implement these recommendations, with the objective of establishing the United States Department of the Space Force by 2020,” he said.

He said that a new position would be created for an assistant secretary of defense for space.

“Creating a new branch of the military is not a simple process. It will require collaboration, diligence, and above all leadership. As challenges arise and deadlines approach, there must be someone in charge who can execute, hold others accountable, and be responsible for the results,” he said.

But the move has faced some signs of skepticism from the Defense Department. In a letter to Congress last year, Secretary James Mattis said he opposed the idea of a separate force, arguing that it would “likely present a narrower and even parochial approach to space operations” and said that a “properly integrated approach is better for carrying out this mission.”

“We have not done cost estimation yet,” Deputy Defense Secretary Patrick M. Shanahan told reporters. Asked to give a rough estimate, Shanahan said, “I would assume it's billions,” but would not be more specific. He said the Pentagon likely would have a firmer estimate by November.

Earlier this week, Mattis signaled his support for a new Space Command to take place alongside existing commands, but demurred when asked about the creation of a separate service entirely, saying it was a matter for Congress to decide.

He did, however, say the Pentagon was in “complete agreement” with the White House.

“We are working our way through all this. We are in compete agreement, the vice president is the point man for the president on this, we are working closely, daily with his office and with supporters on Capitol Hill and the relevant committees,” he said. “So we’re working it up what that actual organization will look like.”

“It will be fit for purpose is what I can assure you, but I don’t have all the final answers yet, we’re still putting that together,” he said.

Fox News’ Lucas Tomlinson, Blake Burman and The Associated Press contributed to this report.