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.

The eight experts who make up the panel all come from different countries and possess specific expertise in areas like 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 United Nations 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 al-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.

“We knew stuff was going on,” Mr. Newcomb said. “We really wanted to up the game on chemical weapons programs, and we just weren’t able to get what we needed to do so.”

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 United Nations 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 American and other spy services.

North Korea’s relationship with Syria takes up one section of the report, which also documents the many ways the government of North Korea’s leader, Kim Jong-un, has tried to circumvent sanctions. It describes how North Korea uses a complex web of shell companies and sympathetic foreign citizens to gain access to international financing, employs sophisticated cyber operations to steal military secrets and enlists its own diplomats in smuggling operations.

It also criticizes Russia and China for failing to do enough to enforce sanctions on items like oil, coal and luxury goods.

The sanctions, it says, have yet to be matched “by the requisite political will, international coordination, prioritization and resource allocation necessary to drive effective implementation.”

The report gives fresh details of a military relationship between North Korea and Syria that goes back decades. During the Arab-Israeli wars in the 1960s and 1970s, North Korean pilots flew missions with the Syrian Air Force. Later, North Korean technicians helped to develop Syria’s arsenal of ballistic missiles and to build a nuclear power plant capable of producing plutonium, which can be used to make nuclear weapons. Israel destroyed the plant in 2007.

In 2015, Syria honored that assistance by opening a monument and park in Damascus dedicated to North Korea’s founder, Kim Il-sung, grandfather of the current leader. The unveiling ceremony, held as Syria’s civil war raged, featured North Korean and Syrian dignitaries, military officials and a marching band.

North Korea has provided training and support for Syria’s chemical weapons program since at least the 1990s, according to a forthcoming book by Bruce Bechtol, a former Korea analyst at the United States Defense Intelligence Agency who is now a professor at Angelo State University in Texas. The book also describes an accident in 2007 in which several Syrian technicians, along with North Korean and Iranian advisers, were killed in the explosion of a warhead filled with sarin gas and the extremely toxic nerve agent VX.

The relationship with Syria “has been a boon for the North Korean military-industrial complex,” Mr. Bechtol said in an interview.

The United Nations report says the cooperation continued during Syria’s civil war, despite international sanctions. Crucial evidence of that was found in January 2017, when two ships carrying acid-resistant tiles, commonly used in the construction of chemical weapons factories, were interdicted at sea en route to Damascus, the report said.

Those shipments were among five deliveries agreed to in a contract between a government-owned company in Syria and the Korea Mining Development Trading Corp., a North Korean company involved in arms exports, according to the report. It based those findings at least in part on copies of contracts provided by the shipping company, identified as Cheng Tong Trading Co. Ltd., based in China.

The report said the three other shipments had been sent between Nov. 3 and Dec. 12, 2016.

The report did not say which country interdicted the two January tile shipments or whether the other three shipments were delivered to Damascus. The contract stipulated that the materials were to be delivered to the Metallic Manufacturing Factory, a company run by the Syrian government that was penalized by the United States Treasury Department last year for its involvement in Syria’s weapons industry.

Several months earlier, in August 2016, a delegation of North Korean missile technicians visited Syria, at which point there was a transfer of “special resistance valves and thermometers known for use in chemical weapons,” the report said, without elaborating. An unidentified United Nations member country told the report’s authors that North Korean missile technicians worked at Syrian chemical weapons and missile facilities in Barzeh, Adra and Hama.

In 2013, after the Obama administration threatened military action in response to a sarin gas attack on the rebel enclave of Ghouta that some experts estimated killed 1,400 people, Mr. Assad agreed to destroy his stockpile and join the Chemical Weapons Convention, which comprises 192 countries that are to have dismantled their chemical weapons programs.

But Western officials and nonproliferation experts have long suspected that Mr. Assad retains some chemical weapons.

So far this year, according to diplomats and witnesses, several chlorine gas attacks have occurred in rebel-held areas in Ghouta, Idlib and Afrin. A separate United Nations panel also said Mr. Assad’s forces were responsible for a sarin gas attack on the rebel-held village of Khan Sheikhoun last April that killed at least 83 people and sickened roughly 300.

Mallory Stewart, a former State Department official who was involved in the Obama administration’s efforts to dismantle Syria’s chemical weapons program, said that there were always concerns that the Assad government had not listed all of its chemical weapons stockpile on its declared inventory of what it gave up. The report, she says, “confirms everything we’ve been saying.”

“Certainly what we tried to do in the last administration is dismantle the entire chemical weapons program,” Ms. Stewart said, “which we know they never did.”

Establishing the origins of such weapons has been difficult. In November, Russia used its Security Council veto to end the work of an independent panel investigating chemical weapons used in the Syrian conflict. The Joint Investigative Mechanism, as it was known, had found that both the Syrian government and Islamic State militants had used chemical weapons in the war, though Russia’s ambassador to the United Nations labeled the panel’s reporting “a joke.”