Hezbollah, the Lebanese militant group, planned to assassinate the former Israeli prime minister Ehud Olmert to avenge the killing of one of its senior military leaders by the Mossad secret service, it has been reported.

The plot was reportedly thwarted because a Hezbollah security official was working undercover for the Israelis and tipped them off in advance. The date or location of the alleged attack were not published.

Al-Arabi al-Jadeed, a London-based Arabic daily newspaper, broke the sensational-sounding but hard-to-verify story about clandestine warfare between bitter enemies from Beirut, attributing it to unnamed political sources with close links to Hezbollah.

Neither Israeli nor Hezbollah officials commented on the report, but there has been partial confirmation from an Israeli newspaper report that security around Olmert, now retired, had been tightened a year ago due to fears of possible retaliation for the killing of Imad Mughniyeh in Damascus in 2008. Haaretz gave no source for its story. As prime minister, Olmert launched Israel’s invasion of Lebanon in 2006.

Mughniyeh, Hezbollah’s military chief, was held responsible for deadly attacks on American and Israeli targets in Lebanon and abroad over two decades. Until the emergence of Osama Bin Laden and al-Qaida in the 1990s he was probably the most wanted man in the Middle East.

Mughniyeh was walking down a Damascus street in February 2008 when a bomb planted in a parked SUV exploded, killing him. Prior to the blast, a team of CIA spotters were monitoring his movements in the Syrian capital as Mossad agents remotely triggered the bomb from Tel Aviv, according to a recent detailed report in the Washington Post.

Al Araby al-Jadeed said the plan to kill Olmert, who was Israel’s prime minister in 2008, was not carried out due to information provided by Mohammad Shawraba, a senior official in the external operations branch of the Iranian-backed Shia organisation.

Shawraba was arrested several months ago by Hezbollah’s internal security force and is said to have admitted to collaborating with Israel. Arab media have said he foiled attacks against Israeli targets in Azerbaijan, Turkey, Cyprus and Peru, with the information that he is said to have provided to Israel. In 2012 a suicide bombing attack that killed five Israeli tourists and a Bulgarian was blamed on Hezbollah.

Shawraba, a businessman, was recruited by the Mossad in a “western Asian country”, according to a December report in the Lebanese daily al-Nashra.

Hezbollah has not commented on those reports but has acknowledged that Shawraba was arrested and admitted working with Israel. Hassan Nasrallah, the group’s leader, acknowledged this openly three weeks ago in an interview.

According to the Washington Post, which quoted former US officials, the CIA and the Mossad were jointly responsible for the assassination of Mughniyeh. Last month, Mughniyeh’s son, Jihad, also a high-ranking Hezbollah operative, was killed in an air strike in Syria that was widely attributed to Israel. A senior Iranian Revolutionary Guard commander died in the same attack.