CAIRO — It was one of the most shocking episodes of recent fighting in Libya, and the United Nations seemed determined to get to the bottom of it.
A 13-page report published last week described in stark detail the bombing in July of a detention center in the town of Tajoura, near Tripoli, which killed 53 people, mostly African migrants. The United Nations report featured testimony from survivors, measured the bomb crater and called for an investigation into a possible war crime.
What it conspicuously failed to do, though, was identify the perpetrator. “A foreign state,” investigators concluded.
The United Nations’ reluctance to identify or even hint at who was behind the bombing is symptomatic, analysts say, of the weakness of its nine-year-old arms embargo on Libya, one so widely flouted that the body’s envoy to Libya last year said that it risked becoming a “cynical joke.”
At least six foreign nations are fueling the mayhem in Libya, supplying weapons, mercenaries or military advisers to rival factions battling for control of the oil-rich country.
But none of these outside actors has ever been held to account, avoiding scrutiny by exploiting either international divisions over Libya or their ties to Western powers like the United States. Sometimes they manage to avoid mention at all.
The unnamed foreign state behind the July attack, according to four United Nations officials, was the United Arab Emirates, an American ally and the main backer of Khalifa Hifter, the commander whose forces have been laying siege to Tripoli, the capital, since April.
The officials said a preponderance of technical and circumstantial evidence pointed to the Emirates, including the fact that its French-built Mirage warplanes are able to carry out the sort of night strike that devastated the detention center.
The Emirates is also, perhaps, the most egregious violator of the embargo, imposed in 2011 as Libya plunged into civil war after the ouster of Col. Muammar el-Qaddafi.
But other nations have inserted themselves in the fighting as well. On Mr. Hifter’s side, the United Arab Emirates is joined by Russia, Egypt, Jordan and France. Turkey has sided with the beleaguered Tripoli government.
United Nations inspectors publish reports every year documenting the profusion of weapons that foreign states have injected into the Libyan battlefield: warplanes, armed drones, laser-guided artillery, missile defense systems and a huge volume of small arms.
Yet none face any real risk of punishment, or even censure. Since 2011, the inspectors have submitted dossiers with details of embargo violations by numerous countries, including the Emirates, to a Security Council sanctions committee, two officials said.
But only two non-Libyans — a pair of Eritrean citizens accused in 2018 of people smuggling — have been penalized for their actions in the war.
The failures of the embargo have been thrown into stark relief since Jan. 19, when world leaders met in Berlin to sign a 55-point declaration that pledged to push for a cease-fire in Libya and uphold the arms ban. No sooner had the ink dried on the agreement than more weapons flooded into Libya, apparently in preparation for a fresh round of fighting.
Turkish warships moved into Libyan waters last Wednesday, escorting a cargo ship said to be carrying armored vehicles for the Tripoli government. Turkey has already deployed Syrian mercenaries, estimated in the thousands, to the fight.
And in eastern Libya, dozens of cargo planes have arrived at an air base controlled by the United Arab Emirates, prompting speculation that they were carrying reinforcements for Mr. Hifter.
The blatant breaches of the embargo since the Berlin agreement prompted a furious outburst on Thursday by the United Nations envoy to Libya, Ghassan Salamé.
In a speech to the Security Council, Mr. Salamé railed against “unscrupulous actors” who “cynically nod and wink toward efforts to promote peace and piously affirm their support for the U.N.” even as they “double down on a military solution, raising the frightening specter of a full-scale conflict and further misery for the Libyan people.”
Mr. Salamé’s words appeared to be directed at President Recep Tayyip Erdogan of Turkey and the de facto leader of the Emirates, Prince Mohammed bin Zayed, both of whom signed the Berlin declaration.
The world’s wavering attention to Libya was rekindled in July by the bombing of the militia-run detention center, which made victims of scores of African migrants who were effectively trapped in the country’s turmoil. In addition to the 53 deaths reported by the Libyan authorities, more than 80 people were wounded.
Since Mr. Hifter, a former Qaddafi-era general and onetime C.I.A. asset, launched his assault on Tripoli in April, fighting has killed at least 2,200 combatants and civilians while displacing more than 300,000 people. Oil prices were affected after Mr. Hifter’s forces cut off most of Libya’s oil production.
The Emirates is Mr. Hifter’s main military backer and has been identified in successive reports by United Nations investigators as a leading violator of the arms embargo. Yet it has evaded penalty, even when it is accused of killing civilians, by successfully leveraging its ties with powerful allies like France and the United States.
“There is an omerta on the role of the U.A.E., and it’s purely political,” said Wolfram Lacher, an analyst at the German Institute for International and Security Affairs and the author of a new book, “Libya’s Fragmentation.”
“Nobody,” Mr. Lacher said, “wants to strain ties with the U.A.E. over its role in Libya.”
A spokesman for the United Arab Emirates, which officially denies any role in Libya’s war, declined to comment on accusations that it was responsible for the detention center bombing.
Critics accused the United Nations mission to Libya and its human rights commission, which co-wrote the report on Tajoura, of going soft on the war’s foreign meddlers by failing to single them out.
“The failure to name names is really disturbing,” said Sarah Leah Whitson of the Quincy Institute for Responsible Statecraft, a foreign policy research body. “The U.N. should go out of its way to demonstrate that it’s not holding back in terms of identifying the weapons smugglers and embargo breakers.”
A spokesman for the United Nations mission said it had published everything it knew about the episode.
Privately, officials say that a high evidentiary threshold and the challenge of obtaining reliable information in Libya make it hard to definitively identify the perpetrators of some attacks, such as the one in Tajoura.
But more broadly, they add, their actions are hampered by the intense international jockeying over Libya.
When it comes to investigating embargo violations, powerful Western countries like the United States and Britain are reluctant to share intelligence on Libya, United Nations officials say, because they do not want to embarrass Arab allies like Egypt or the United Arab Emirates.
Other countries have inserted themselves into Libya’s chaos. Last fall, Russia deployed Kremlin-backed mercenaries to bolster the assault on Tripoli. Among Arab states, Jordan is a major arms supplier to Mr. Hifter while Egypt provides him with logistical and diplomatic support. Unusually, Turkey has openly declared its military support to the Tripoli government, which was approved by a vote in Parliament last month.
France’s role in Libya has also come under scrutiny. Last week President Emmanuel Macron accused Turkey of reneging on a promise to get out of Libya. But Mr. Macron himself has faced charges of meddling there, albeit on the other side of the fight.
American policy in Libya has appeared noncommittal under President Trump, except when it comes to fighting the Islamic State or condemning the increased Russian role in the war.
At the same time, though, American officials have often appeared to give cover to the actions of their Emirati allies. As fighting escalated on Thursday, a senior Pentagon official, Gen. Stephen J. Townsend, gave congressional testimony that sharply criticized Turkish and Russian intervention but failed to mention the United Arab Emirates.
Mr. Salamé, the United Nations envoy, warned last year that without action to halt the flow of arms into Libya, the country would descend into a “Hobbesian all-against-all state of chaos,” and eventually be partitioned.
The Berlin conference in January stoked hopes for a different path. But now, as both sides gird for more fighting, those hopes are dimming.
Eric Schmitt contributed reporting from Washington.