North Korea has produced a miniaturized nuclear warhead that can fit inside its missiles, a crucial technological breakthrough on the path to becoming a nuclear power, The Washington Post reported Tuesday.

The Defense Intelligence Agency completed the confidential analysis in July, shortly after another intelligence assessment that sharply raises the official estimate for the total number of bombs in the communist country’s atomic arsenal, the Post says. 

The DIA did not immediately respond to USA TODAY’s request for comment on the report.

That assessment calculated last month that up to 60 nuclear weapons are now controlled by North Korean leader Kim Jong Un. The Post points out that some independent experts believe the number of bombs is much smaller.

The DIA ‘s latest assessment comes against a backdrop of growing international concern regarding North Korea’s nuclear and missile testing. China, Pyongyang’s biggest supporter, on Sunday urged North Korea to halt its testing, and on Saturday China and Russia joined with the United States in a unanimous U.N. Security Council vote approving the toughest economic sanctions yet against the increasingly isolated regime.

The sanctions target about a third of North Korea’s estimated $3 billion in annual exports. 

Still, the U.S. has expressed a willingness to work with Korean leader Kim Jong Un. U.S. Secretary of State Rex Tillerson said last week that the U.S. was not…