A group of CIA informants in Lebanon were captured earlier this year by Hezbollah, U.S. officials said Monday, damaging agency operations against an organization with long-standing ties to terrorism and raising concern that spies who had spent months or years on the CIA payroll could be tortured or killed.

The breach has forced the CIA to suspend some of its espionage efforts in a country that has long been a crossroad for spy services and to launch a damage-assessment effort to determine if other assets — or even CIA case officers stationed in Beirut — are in jeopardy.

Current and former U.S. officials said the identities of as many as a half-dozen informants appear to have been betrayed by cellphone records and calling patterns, underscoring the sophistication of Hezbollah’s counterintelligence efforts as well as the hazards of espionage in an age when even CIA assets can be tripped up by a data trail.

CIA veterans familiar with the exposure described the harm as extensive. “It has caused irreparable damage to the agency’s ability to operate in the country,” said a former CIA official with knowledge of the case. The former official attributed the failure to a breakdown in tradecraft. “It is all a result of bad counterintelligence tactics.”

A U.S. official who had been briefed on the case disputed that characterization, saying that the damage to CIA intelligence gathering was limited and that the agency has long treated Hezbollah as a sophisticated adversary.

“The assertion that CIA activities in Beirut are shut down is nonsense,” said the official, speaking on the condition of anonymity to discuss intelligence matters. “Collecting sensitive information on adversaries — who are aggressively trying to uncover spies in their midst — will always be fraught with risk.”

Preston Golson, a CIA spokesman, declined to comment on the matter. “The CIA does not, as a rule, discuss allegations of operational activities,” he said.

The CIA does not believe that any informant has been killed or that any case officer in the country has been identified. But U.S. officials acknowledged that the fate of those captured — likely Lebanese nationals— remains unclear.

Former U.S. officials said the spies were part of a broader network of informants recruited by the CIA and paid to provide information on Hezbollah, which is listed as a terrorist organization by the U.S. government.

The CIA gathers intelligence on Hezbollah’s ties to terrorism, the capabilities of its military wing, its links to Iran and its expanding political influence in Lebanon. The organization is a major target of Israeli intelligence as well.

Hezbollah is “a determined terrorist group, a power political player, a mighty military and an accomplished intelligence organization — formidable and ruthless,” said the U.S. official who spoke on the condition of anonymity. “No one underestimates its capabilities.”

The roll-up of CIA informants had been a subject of speculation since June, when Hezbollah’s leader, Hassan Nasrallah, claimed in a television address that his counterintelligence forces had identified at least two CIA spies.

Current and former U.S. officials said Hezbollah appears to have been able to access and exploit cellular phone records to root out spies.

“Hezbollah was able to identify all the cellphones of all the assets in the country,” said the former agency official with knowledge of the case, using the CIA term for a paid overseas informant. “Hezbollah was able to isolate where people were by looking at the cell records. They could tell where and when people were meeting.”

Officials said it is unlikely that examining phone records alone enabled Hezbollah to uncover the spy ring. Instead, the scrutiny of the records may have been a follow-up to suspicion of someone within Hezbollah or resulted from the use of a “dangle” — a double-agent who volunteers to work for the CIA in hopes of penetrating its ranks.

“Somehow, something tipped them off that they had a problem inside their organization,” said a former CIA official with experience in the region. “Someone being monitored made calls that made no sense, and they reverse-engineered that to [identify other informants] in their organization.”

Staff researcher Julie Tate contributed to this report.