Washington (CNN) In a series of unusually candid remarks, the US general in charge of the nation's nuclear arsenal has issued a stark warning that Russia and China are "aggressively" developing new high-speed, or hypersonic, weapons that the US currently has no defense against.

The weapons might not be operational for several years, but Gen. John Hyten, the four-star head of US Strategic Command , is warning that changes to missile defenses are urgently needed or the US will be unable to detect them when they are operational.

"China has tested hypersonic capabilities. Russia has tested. We have as well. Hypersonic capabilities are a significant challenge," Hyten told CNN in an exclusive interview. "We are going to need a different set of sensors in order to see the hypersonic threats. Our adversaries know that."

Hyten and other military officials say the current generation of missile detecting satellites and radars won't be enough to detect these new generation weapons. Hypersonic is generally defined as a speed of Mach 5 or over 3,806 miles per hour.

"We've watched them test those capabilities," Hyten told Congress last week. But with unusual public candor about potential US military shortfalls, he acknowledged "we don't have any defense that could deny the employment of such a weapon against us, so our response would be our deterrent force, which would be the triad and the nuclear capabilities that we have to respond to such a threat."

Read More