Iran is suspected of continuing to cooperate with North Korea on missile development, a recent US congressional report said after the communist nation carried out a surprise test of a submarine-launched ballistic missile.

The Congressional Research Service report, published on Tuesday, raised the suspicions while noting that the two countries have cooperated on a wide range of military and weapons of mass destruction-related activities in the past, particularly the development of ballistic missile technology.

"It is widely suspected that the two continue to cooperate on missile development, and possibly nuclear issues as well, but the extent of the cooperation, if any, is not known from published sources," the report said.

Citing a 2018 report mandated by the Countering America's Adversaries through Sanctions Act, CRS said that Iran has bought weaponry from North Korea and "has obtained missile and aircraft technology from foreign suppliers, including China and North Korea."

Iran's navy also has 14 Yono-class midget subs designed by the North, the report said.

"In the past, Iran reportedly funded and assisted in the retransfer of missile and possibly nuclear technology from North Korea to Syria," the report also said, noting that the communist state has also supplied Iran with small submarines.

On suspected nuclear cooperation between Iran and North Korea, the report said that "there are persistent reports that Iran-North Korea missile cooperation is extensive," but the report did not provide further details, saying "it is not known whether North Korea and Iran have recently exchanged missile hardware." (Yonhap)