During the 1980s and 1990s, China created the Iranian nuclear weapons program through the sales of complete nuclear and missile facilities, along with dual-use and unfinished technologies.  Yet, in 1997, Bill Clinton told the U.S. Congress that "China has provided clear and unequivocal assurances to the United States that it is not assisting and will not assist any non-nuclear weapon state, either directly or indirectly, in acquiring nuclear explosive devices or the material and components for such devices."

The Clinton administration's foreign policy was a disaster, and Clinton's statement to Congress exemplifies how incompetent his administration was on a range of national security issues.  In fact, Clinton's claim was so dangerous that it directly placed the West on a collision course with a nuclear-armed Iran (and North Korea), irreparably damaging non-proliferation efforts in the process.  Even now, we still see those on both sides of the political spectrum denying China's ongoing role in Iran's nuclear program.

Back in 2006, John Tkacik, a senior research fellow in China policy at the Heritage Foundation, authored a report that concluded the following:

Despite over a decade of protests from Washington, China continues to export nuclear technology, chemical weapons precursors, and guided missiles to Iran.  Indeed, China is one of Iran's top two weapons suppliers (with Russia).  A report in 2004 by the U.S.-China Security and Review Commission stated that "Chinese entities continue to assist Iran with dual-use missile-related items, raw materials and chemical weapons-related production equipment and technology" and noted that the transfers took place after the Chinese government pledged in December 2003 to withhold missile technology [to] Iran.  The Central Intelligence Agency reported in 2004 that "Chinese entities are continuing work on a zirconium production facility at Esfahan that will enable Iran to produce cladding for reactor fuel."  Although Iran was a signatory to the Nuclear Nonproliferation Treaty and was required to accept International Atomic Energy Agency (IAEA) safeguards on its production of zirconium fuel cladding, Iran made no moves to do so, and China exerted no influence to the contrary.

By 2009, the story was the same.  Media reports emerged that "Iran has dramatically stepped up covert attempts to buy nuclear equipment over the last six months, often by using Chinese companies as fronts."  A Chinese company was being charged in a New York court "with knowingly selling missile and nuclear technology to Iran."  And former U.N. IAEA nuclear inspector David Albright, then at the Institute for Science and International Security, was publicly calling on China to cease its involvement in Iran's nuclear program.

Thus, here we are in 2009, more than 12 years after Clinton told Congress that China purportedly ended involvement with Iranian nuclear weapons ambitions, and open-source reports from across the political spectrum continue to claim that the nuclear pipeline from China to Iran flows onward.

It didn't end there.  As of mid-2011, Reuters obtained a confidential United Nations report that, once again, showed China's duplicitous game at work:

North Korea and Iran appear to have been regularly exchanging ballistic missile technology in violation of U.N. sanctions ... The report said that the illicit technology transfers had "trans-shipment through a neighbouring third country."  That country was China, several diplomats told Reuters on condition of anonymity.

Another damning indictment against China came in late 2013, when three leading U.K. non-proliferation experts from academia and government published the following conclusions:

China continues to be the key source of goods and technology for the prohibited nuclear and missile programs of Iran and North Korea, with some officials estimating that China is used as a transit route for up to 90 percent of goods destined for those programs.  The alleged serial Chinese proliferator Li Fang Wei (aka Karl Lee) reportedly was able to earn more than $10 million from the sale of missile-related items to Iran after the United States indicted him in 2009 on more than 100 criminal counts of falsifying business records related to illicit trade with subsidiaries of an Iranian military agency[.] ...

More recently, the involvement of large state-owned strategic and defense companies has subsided.  Today, the primary source of goods for prohibited programs is China's private sector, particularly small- and medium-sized enterprises that often act as distributors or middlemen in trade with western manufacturers.

Rather than transferring "complete missile systems and nuclear or missile production facilities" to Iran, in order to avoid U.S. condemnation, China now funnels either dual-use technology or materials at quantities below control-list thresholds that would trigger export licensing requirements.  In this manner, the Chinese government attempts to set up a plausible deniability defense, although serious analysts acknowledge that the likelihood of this extensive activity occurring without the knowledge and approval of the central government is effectively zero.

Historically, China used to employ Pakistan for nuclear technology transfer to Iran.  Now that has shifted in large part to North Korea, but the ultimate source remains the same.  As reported in 2014 by Gordon Chang, a noted expert on China:

[The] National Council of Resistance of Iran [NCRI], the dissident group that in 2002 disclosed the heavy-water production facility at Arak and the underground uranium-enrichment plant in Natanz, charged in September 2005 that the Chinese trade in centrifuges continued into that year.  That month, NCRI also accused China of secretly sending beryllium to Iran.  This metal is used in neutron initiators to trigger nuclear weapons, and due to the surreptitious nature of the transfers, it is highly unlikely that Iran bought the material for civilian purposes.  The allegation is consistent with other reports about Iran's covert attempts to source beryllium at that time.  In July 2007, the Wall Street Journal reported that the State Department had lodged formal protests with Beijing about Chinese companies, in violation of the first two Security Council resolutions on Iran, exporting to that country items that could help Tehran build nukes.

Other materials and technologies whose shipment violates international treaties and U.N. rules have been sent to Iran via Chinese state-owned enterprises, a fact that directly links the Chinese government to the transfers.

This point was reinforced by Orde Kittrie in his Foreign Affairs article from mid-2015:

[L]ittle attention has been paid to the longtime leading suppliers of Iran's nuclear program: ostensibly private brokers based in China.  Foremost among them appear to be Karl Lee (also known as Li Fangwei) and Sihai Cheng, who, according to U.S. federal and state prosecutors, have shipped vast quantities of key nuclear materials to Iran.  Even at the peak of international sanctions against Iran, China has reportedly made little to no effort to stop these or other such brokers.

Although China claims otherwise, it seems likely that the Chinese government uses these so-called private brokers as proxies to assist Iran's nuclear program.  In that way, Beijing can both benefit from the illicit transactions with Iran and appear an adherent of various nonproliferation agreements[.]

One hopes that the current administration – with respected geopolitical realists such as John Bolton and Fred Fleitz – will take concrete action to halt Iran's program and pressure China over its long-term support.  A narrow window is available in which to take a strong foreign policy stance against China's nuclear proliferation efforts.  Suitable sanctions must be placed against both countries, and the dangerous track that the Clinton, Bush, and Obama administrations collectively set us along – and in which the rest of the West was complicit – must be rolled back.