North Korea and Iran have resumed long-range missile cooperation, which includes the transfer of critical parts, Reuters reported Monday, citing a senior US official who did not provide detailed evidence.

The official, who was speaking of a broader US plan to sanction people and entities linked to Iran’s weapons programs, did not elaborate on when Pyongyang and Tehran first started working together, or when they stopped and began again, according to the report.

North Korea and Iran have forged close ties against the United States and have long been suspected of cooperating to build ballistic missiles and nuclear weapons.

In March last year, the US Congressional Research Service wrote that North Korea and Iran were believed to be cooperating on missile and nuclear weapons programs, but said it was not sure how extensive that joint work was with the available information.

The Congressional Research Service said Pyongyang was only one of a few partner countries involved in military exchanges with Tehran, having provided it with a small submarine in the past.

The US can independently sanction individuals and groups tied to the North’s arms programs, in addition to the existing UN sanctions.

Speculation is mounting over the possibility of a North Korean missile launch around the founding anniversary of the ruling Workers’ Party on Oct. 10, with some experts expecting the regime to showcase missiles at a military parade on the day of anniversary.

“The North Koreans are going to come out potentially with scores of solid propellants, medium range missiles, maybe Pukguksong-2s,” Ankit Panda, a senior fellow at the Carnegie Endowment for International Peace, told a teleconference hosted Wednesday a week earlier by the Korea Society.

“(North Korea) will parade those down at Kim Il-sung Square in a way they’ve never done before.”

The Center for Strategic and International Studies also said it was expecting the North to soon fire a submarine-launched ballistic missile, though it added that the evidence was inconclusive.

South Korea’s Defense Minister Suh Wook said he saw little chance of a launch amid the coronavirus outbreak and recent floods that battered the isolated country.