"I think, it's probably a matter of a couple of years," Esper said in the interview with Fox News released on Wednesday when asked how close the United States was to creating its hypersonic weapon.
Earlier this week, US Acting Army Secretary Ryan McCarthy argued that Washington was seeking to develop a hypersonic ballistic missile with a radius range that had previously been banned by the US-Russian Intermediate-Range Nuclear Forces Treaty (INF), which collapsed on August 2.
In February, the United States formally suspended its INF obligations, triggering a six-month withdrawal process. In July, Russian President Vladimir Putin followed suit by signing a decree suspending Moscow's participation in the accord. The sides had been accusing each other of violating the treaty.