The Islamic Republic's aerospace industry has depended on North Korean -- as well as Chinese and Russian -- technology and expertise to develop its strategic missile force, generally seen as a means of delivering the nuclear warheads that the United States and its allies say Tehran is driving to produce.
The April 13 launch in North Korea of a long-range Unha-3 rocket ended when the much-hyped rocket crashed into the Yellow Sea shortly after launch.
That's not likely to enhance Pyongyang's reputation with the Iranians, who have had similar setbacks themselves in tests in the Dasht-e Kavir, the Great Salt Desert south of Tehran.
North Korea said the three-stage Unha was meant to put a communications satellite in orbit. But U.S., South Korean and Japanese officials said the launch was part of North Korea's drive to develop an intercontinental ballistic missile.
The launch was observed by a 12-man team of ballistic missile engineers from Iran's Shahid Hemmat Industrial Group, which builds Iran's ballistic missiles outside Tehran.
SHIG is part of Iran's state-run Aerospace Industries Organization. It's responsible for liquid-fueled ballistic missiles such as the Shehab-3, which is based on North Korea's No-Dong system and which kick-started Iran's entire missile program more than a decade ago.
South Korea's Yonhap news agency reported that the Iranians had arrived in Pyongyang March 31 "undoubtedly to observe the missile launch and receive test data" from the North Koreans.
North Korea has played a vital role in helping the Iranians develop their missile program, assistance that may carry over into Tehran's quest for nuclear warheads.
Both Pyongyang and Tehran, opposed to the United States and Israel, have been driving to develop intercontinental ballistic missiles, defined by the United States as weapons with a range greater than 3,400 miles.
In November 2010, there were persistent reports than North Korea had provided Iran with 19 advanced BM-25 missiles capable of carrying nuclear warheads. U.S. diplomatic cables released by WikiLeaks stated that Iran's technological capabilities would be greatly advanced by acquisition of these systems and allow them to develop a whole new generation of missiles.
The BM-25 is modeled on the Russian submarine-launched R-27, built by the Makeyev Design Bureau, which also built the ubiquitous Scud-B, the model for North Korea's liquid-propelled missile systems.
The BM-25, known to NATO as the SS-N-6, has an estimated range of 1,500 miles. At that time, the maximum range of Iran's indigenous missiles was around 1,250 miles.
The BM-25 is longer and heavier and carries more fuel, adding up to a range of as much as 2,000 miles, enough to hit Western Europe -- or Moscow.
This came at a time when Western concerns were mounting about Iran's increasingly sophisticated ballistic missile program after Tehran lofted its first satellite into space aboard a booster rocket, the Safir, that had a more powerful engine than previous systems and contained some of the Russian technology.
Converting booster rockets for space launches to long-range ballistic missiles is a key building block toward intercontinental capabilities.
"Iran wanted engines capable of using more energetic fuels," one cable dated Feb. 24, 2010, said, "and buying a batch of BM-25 missiles gives Iran a set it can work with on reverse engineering."
The BM-25 transfer hasn't been verified. But the missiles are believed to have been delivered to Iran in 2005, before U.N. sanctions on Pyongyang were imposed its nuclear tests in 2006 and 2009.
All in all, the cables indicated a much stronger military cooperation between the two states than had been publicly known.
Last May 13, a U.N. panel of experts submitted a report to the U.N. Security Council that said Pyongyang had persisted in exporting ballistic missiles, missile components and associated technologies to Iran "in an effort to get hard currency and to advances its own efforts."
It said North Korea, excluded by the United Nations from trading in nuclear and missile technology, was illegally shipping these banned materials "through a neighboring third country," suspected to be China.