The Biden administration launched a behind-the-scenes push last month to reach out to North Korea through multiple channels, a senior administration official has told CNN, but thus far Pyongyang has been unresponsive, CNN reported.

"To reduce the risks of escalation, we reached out to the North Korean government through several channels starting in mid-February, including in New York," the official said. "To date, we have not received any response from Pyongyang. This follows over a year without active dialogue with North Korea, despite multiple attempts by the US to engage."

The official did not provide further details of what the outreach entailed, but noted the administration has been conducting its interagency review of the United States' policy towards North Korea, "including evaluation of all available options to address the increasing threat posed by North Korea to its neighbors and the broader international community."

"We look forward to completing our intensive, multi-stakeholder policy review in the coming weeks," the official said.

Satellite imagery obtained by CNN reveals North Korea has recently taken steps to conceal a facility that US intelligence agencies believe is being used to store nuclear weapons.