Intelligence officials and nuclear experts say Iran and North Korea have both made "significant progress" developing nuclear weapons programmes in the past year, the New York Times reported on Sunday.
US officials want to step up covert actions to stall Iran's alleged nuclear arms efforts, "in a tacit acknowledgement that the diplomatic initiatives with European and Asian allies have failed to curtail the programmes," the daily said.
Meanwhile "North Korea now probably has enough weapons-grade plutonium to test a weapon in the future," despite toughened sanctions and several rounds of six-nation talks aimed at curtailing such efforts, the Times said.
The assessment comes from a new classified intelligence report, described to the Times by people who read it, which "appears to have been written far more cautiously than the National Intelligence Estimate that erroneously described advanced weapons programmes in Iraq."
North Korea is thought to have "completely reprocessed" all of its weapons-grade plutonium, according to non-proliferation expert Gary Samore.
"They had a huge window of opportunity when we were invading Iraq, and they appear to have made maximum use of it," he told the Times.
Furthermore, both the Iranian and North Korean weapons programmes are increasingly self-sufficient thanks to aid they received from Pakistani scientists, the daily said.