North Korea launches what it claims was a hypersonic missile, Jan. 5, in this photo provided by the North Korean government. North Korea actually launched an intermediate-range ballistic (IRBM) missile into the East Sea, South Korea's military said, raising fears that Pyongyang was inching toward its threatened suspension of a self-imposed moratorium on nuclear weapons and long-range missile tests. AP-Yonhap

North Korea does not appear to have developed a hypersonic missile, but its tests to develop such a system warrant U.S. concern, the head of the U.S. Missile Defense Agency said Wednesday.

Pyongyang claims it successfully tested a new hypersonic missile, Jan. 5 and Jan. 11 (KST).

"They claim to have developed hypersonics," Vice Adm. John Hill said when asked if the North was developing hypersonic missiles in a hearing before the Senate Subcommittee on Strategic Forces.

"But in terms of what we have seen, in terms of data, I'm not entirely confident that they have that capability today, but the fact that they are testing it ought to be of concern," he added.