HUNTSVILLE, Ala. — The Pentagon's top engineer criticized Russia and China this week for militarizing space, a move the Trump administration wants to address with the formation of a sixth service branch dubbed Space Force.

His remarks came a day before Vice President Mike Pence laid out President Donald Trump's vision for creating the Space Force by 2020.

"We are not the people who choose to weaponize space, but if we are challenged we will respond," Michael Griffin said Wednesday at the Space and Missile Defense Symposium in Huntsville, Alabama. "The Defense Department is today working on a means to defend our existing capabilities and we will be working on methods to project our national power onto our adversaries."

Griffin, a former NASA administrator, explained that Russia and China's pursuit of hypersonics, a kind of weapon the U.S. currently cannot defend against, has prompted the Pentagon to accelerate its development of space-based systems.

"It is our adversaries, not us, who have chosen to weaponize this type of capability," Griffin said, adding that the U.S. would not be eclipsed by Russia and China.

Griffin's comments came on the heels of Chinese reports announcing the first successful testing of a hypersonic aircraft, a feat the U.S. has yet to accomplish.

When asked about China's sprint to deploy this new breed of weapon, Griffin described Beijing's efforts as "much more thoughtful" compared with Moscow's developments.

"The Chinese have been much more thoughtful in their systems development because they are developing long-range tactical precision-guided systems that will be really influential in a conventional fight," Griffin said. "The Chinese ability to hold our forward deployed assets at risk with very high speed and very hard to intercept precision-guided systems is something to which we have to respond," he added.

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Turning to Russia, Griffin noted that Moscow's intercontinental ballistic missiles, or ICBMs, pose a greater threat to the U.S. than the hypersonic weapons Russian President Vladimir Putin purports to have.

In March, Putin debuted new nuclear and hypersonic weapons, which he described as "invincible" during a state of the nation address. The weapons included a nuclear-powered cruise missile, a nuclear-powered underwater drone and a new hypersonic missile.

"We are hostage to Russian ICBMs and they are hostage to ours and maybe I'm missing something, but I do not see what a hypersonic nuclear missile brings to the strategic missile posture that earlier systems don't," he added, referring to Russia's nuclear deterrence.

Griffin's comments followed the top U.S. nuclear commander's warning Tuesday that Russia and China are not "friends" of the United States amid the budding arms race.

"You can't call them [Russia and China] our friends if they're building weapons that can destroy the United States of America and, therefore, we have to develop the capability to respond," Air Force Gen. John Hyten, commander of U.S. Strategic Command, said Tuesday at the Space and Missile Defense Symposium.

Hyten added that the Pentagon has nearly a dozen programs tasked with developing and defending against the new breed of weapons.

"I always wish we started [working on hypersonics] five years ago or 10 years ago because then we wouldn't be worried ... but we didn't so we have to step up now, and we are," he added.