Iranian scientists and military officers will attend North Korea's test launch of a long-range ballistic missile expected this month, underlining Tehran's close and long-standing links to Pyongyang on missile development.

Western diplomatic sources say an engineering team from the Shahid Hemmat Industrial Group, the Iranian organization that developed the Shehab-3 ballistic missile which constitutes the backbone of the Islamic Republic's strategic missile force, will be on hand for the North Korean test scheduled for sometime Dec. 10-22.

The Shehab-3 is based on North Korea's Nodong missile, while more advanced and longer-range ballistic weapons, identified as the Shehab-5 and Shehab-6, are understood to be modeled on Pyongyang's Taepodong series.

Shahid Hemmat Industrial Group, known to Western missile experts as the "SHIG team," is part of Iran's Aerospace Industries Organization, which is controlled by the elite Islamic Revolutionary Guards Corps as part of its Iran missile and nuclear programs mandate.

For more than a decade, Iran and North Korea maintained what is in effect a joint missile development program. Iranian teams have observed all of North Korea's long-range missile tests in 1998, 2006, 2009 and the last one April 13, which was a failure and probably curtailed Iranian efforts.

Iranian teams have been present at North Korean nuclear tests, at least those conducted in 2006 and 2009, both times after failed missiles tests.

More ominously, Japan's Kyodo news agency, citing Western diplomatic sources, reported Friday that Iran stationed military personnel in North Korea in October at a military facility 53 miles from the Chinese border, apparently to strengthen cooperation in missile and nuclear development.

Western security sources say an unknown number of North Korean and Chinese missile technical experts work at the Shahid Hemmat complex, including the missile plant, outside Tehran on the Damavand highway northeast of the city.

In July 2001, Ali Mahmudi Mimand, one of Iran's top aeronautical engineers and purportedly the brains behind the ballistic program, reportedly died under mysterious circumstances.

Western sources said Mimand was killed in an unexplained explosion at the SHIG facility while tests were being carried out on advanced launch apparatus for the Shehab-3 then being developed.

It's not clear whether that was connected to the campaign of sabotage and assassinations carried out by the United States and Israel against Iran's missile and nuclear programs, which has escalated since then.

The United States has twice imposed sanctions on Shahid Hemmat for its role in developing ballistic missiles that could eventually be armed with nuclear warheads.

Iran's program to develop liquid-fuel missiles has been linked to North Korea since it began in the early 1990s with the purchase of Soviet-designed Scud-B and -C missile maintenance and assembly facilities from Pyongyang.

The International Institute for Strategic Studies, a London think tank, notes: "Tehran's decision to procure the Nodong missile ... rather than design, develop, test and produce a more capable missile based on a cluster of four Scud engines suggests that its technical wherewithal and indigenous missile capabilities were at that time limited.

"However, shortly after the turn of the century, Iranian engineers began asserting greater independence from foreign supply, starting with the major, foreign-assisted redesign of the Shehab-3, which resulted in the longer range Ghadr-1."

Oil-rich Iran provided much of the financing for the Nodong program by destitute North Korea, for which the technology transfers were part payment.

U.S. diplomatic cables published by WikiLeaks in February 2010 stated U.S. intelligence was convinced North Korea sold Iran at least 19 BM-25 ballistic missiles.

This missile is based on the Russian SS-N-6 submarine-launched ballistic weapon and was unveiled in Pyongyang in October 2007.

That was seen as proof that Pyongyang was developing its ballistic weapons capability despite U.N. sanctions.

Tehran's acquisition of the BM-25s rang alarm bells in the West, because, if the technology could be refined, "the BM-25 could carry both conventional and nuclear warheads, and with them serious implications for the future security in both the Asia-Pacific region and Europe," Asia analyst Bertil Lintner observed.

The leaked cables suggested "a much closer military cooperation" between Iran and North Korea "than was previously known to the public."