– North Korea has been shipping supplies to the Syrian government that could be used in the production of chemical weapons, United Nations experts contend.

The evidence of a North Korean connection comes as the United States and other countries have accused the Syrian government of using chemical weapons on civilians, including recent attacks on civilians in the Damascus suburb of eastern Ghouta with what appears to have been chlorine gas.

The supplies from North Korea include acid-resistant tiles, valves and thermometers, according to a report by U.N. investigators. North Korean missile technicians have also been spotted working at known chemical weapons and missile facilities inside Syria, according to the report, which was written by a panel of experts who looked at North Korea’s compliance with U.N. sanctions.

The report highlights the potential danger posed by any such trade between Syria and North Korea, which could allow Syria to maintain its chemical weapons while also providing North Korea with cash for its nuclear and missile programs.

The possible chemical weapons components were part of at least 40 previously unreported shipments by North Korea to Syria between 2012 and 2017 of prohibited ballistic missile parts and materials that could be used for both military and civilian purposes, according to the report, which has not been publicly released but which was reviewed by the New York Times.

Neither the report’s authors nor members of the U.N. Security Council who have seen it would comment, and neither would the U.S. mission to the international agency.

It is unclear when, or even whether, the report will be released. “I don’t know about its publication date, if any,” Stéphane Dujarric, a U.N. spokesman, told reporters Tuesday. Asked to comment on the report, he said, “I think the overarching message is that all member states have a duty and responsibility to abide by the sanctions that are in place.”

The eight experts who make up the panel all come from different countries and possess specific expertise in areas such as weapons of mass destruction, maritime transport and customs controls. Since 2010, the panel has had a mandate from the Security Council to investigate possible sanctions violations by North Korea and present its findings in an annual report.

Though experts who viewed the report said the evidence it cited did not prove definitively that there was current, continuing collaboration between North Korea and Syria on chemical weapons, they said it did provide the most detailed account to date of efforts to circumvent sanctions intended to curtail the military advancement of both countries.

William Newcomb, who was chairman of the U.N. panel of experts on North Korea from 2011 to 2014, called the report “an important breakthrough.”

Since the start of the Syrian civil war in 2011, there have been suspicions that North Korea was providing equipment and expertise to maintain the chemical weapons program of Syria’s president, Bashar Assad. Those suspicions were not assuaged when in 2013 Syria signed onto the Chemical Weapons Convention and claimed to give up its chemical weapons stocks.

The report, which is more than 200 pages long, includes copies of contracts between North Korean and Syrian companies as well as bills of lading indicating the types of materials shipped. Much information was provided by unidentified U.N. member states.

The military-related cooperation, if confirmed, indicates major shortcomings in the international effort to isolate both countries. The shipments would have eluded detection even though both nations are subject to highly restrictive sanctions, and are under the intense scrutiny of U.S. and other spy services.