An agent of Israel’s Mossad spy agency infiltrated the upper echelons of Hezbollah’s security apparatus and leaked information about the Lebanese Shiite group for several years before being discovered and arrested recently, according to security officials and people in Lebanon who are familiar with the incident.

The espionage activities of the alleged agent, identified as Mohammed Shawraba, would represent one of the most significant security breaches of the highly secretive organization, which is a mortal enemy of Israel and classified as a terrorist organization by the United States.

The incident, which could not be independently verified, has been widely reported in the Lebanese and Arabic media as having helped Israel thwart numerous Hezbollah operations.

Hezbollah refuses to deny or confirm reports that Shawraba fed the Mossad intelligence on the Lebanese group’s foreign-operations unit, which he had headed since 2008.

“Hezbollah uncovered and arrested Mohammed Shawraba, and they consider his arrest a significant achievement despite the blows that his activities dealt to their operations,” one official familiar with the incident said by telephone, speaking on the condition of anonymity because of a lack of authorization to discuss the issue.

Shawraba was apprehended with assistance from Iranian intelligence, said the official, who added that Hezbollah had become increasingly suspicious of a mole within its highest ranks. Iran, also an enemy of Israel, is Hezbollah’s foremost ally.

Hezbollah and Israel fought a devastating 34-day war in 2006, and the nemeses also have spent years countering each other through acts of espionage. That has involved activities such as Israel’s planting of listening devices on Hezbollah telecommunication networks, including one that exploded in September and killed a member of the group who was attempting to dismantle it, the group said.

Israel is also believed to have been involved in the assassination of Imad Mughniyeh, a senior Hezbollah operative who was killed by a car bomb in Damascus in 2008.

The Bulgarian government formally accused Hezbollah of bombing a bus two years ago that was carrying Israeli tourists in the resort city of Burgas. Hezbollah denies involvement in the attack, which killed six people.

Citing an unnamed security source, the Lebanese English-
language Daily Star reported that Shawraba was being tried in a Hezbollah court. He was arrested with four people who worked for him in the group’s foreign-operations unit, which works against Israeli interests in foreign countries, the newspaper reported. It said Hezbollah had become suspicious of Shawraba after five attempted retaliations against Israel over the Mughniyeh killing had failed.

Lebanon’s Elnashranews Web site also reported that Shawraba, who is believed to come from a village in southern Lebanon, once even headed the security detail for Hezbollah’s leader, Hasan Nasrallah.

Hilal Khashan, professor of political science at the American University of Beirut, said Hezbollah appears to have been caught off-guard by the flurry of news reports about Shawraba. Hezbollah’s response indicates that it wants to reassure supporters that the problem has been resolved, he said.

“Hezbollah’s response to this is very deliberate, and it’s a response that was certainly decided on by the senior leaders, even Hasan Nasrallah himself,” he said.

“The public is now entirely aware of this, and Hezbollah’s response is basically an admission that this happened.”

Mark A. Heller, a research associate at the Tel Aviv-based Institute for National Security Studies, expressed doubt that Hezbollah would retaliate over the issue of an Israeli agent in its organization. The group is too focused on its military operations in Syria, which involve fighting the armed opposition to the regime of President Bashar al-Assad, he said.

“I doubt that at this point they’re interested in an escalation with Israel,” he said.

Hezbollah has previously said publicly that it has been infiltrated by foreign intelligence agencies. In 2011, Nasrallah announced that two Hezbollah members had confessed to working as agents for the CIA.

Suzan Haidamous contributed to this report.