Pyongyang has transferred ballistic missiles and other weapons to Russia, while Iran has also provided Moscow with the supply of Shahed suicide drones, frequently used to attack Ukrainian infrastructure.
In return, Russia has provided technology and supplies that help expand missile and nuclear capabilities of its allies.
Iran has provided well over 1,000 drones since mid-2022, that are often used to swamp Ukrainian air defenses during large-scale missile attacks on civilian targets.
Western powers are increasingly concerned Tehran could soon also transfer ballistic missiles to Russia.
"Russia's friends in Asia are vital for continuing this war of aggression," Stoltenberg said as ministers met in Brussels.
China was also "propping up Russia's war economy," he said.
"This has regional and global security consequences," Stoltenberg said, adding that the ministers would discuss how to handle the issue.
In February, Reuters reported that Iran has provided Russia with a large number of powerful surface-to-surface ballistic missiles, citing six sources, in a sign of deepening military ties between the two US.-sanctioned countries.