Two brothers held in Lebanon as Israeli spies are linked to a team responsible for the assassination of a notorious terrorist leader, Lebanese security sources have claimed.

Ali Jarrah, 50, a Lebanese citizen, and his brother Youssef, from Marj in the Bekaa valley, were arrested last week by the Lebanese army, which charged them with espionage. A third suspect has also been held, sources close to the investigation said. All three face the death penalty.

The spy ring has been linked to the assassination of Imad Mughniyeh, a leading figure in Hezbollah, the Lebanese Shi’ite militia, who was killed in a bomb blast in Damascus in February. Hezbollah’s leader, Sheikh Hassan Nasrallah, blamed Israel for the attack and vowed to take revenge.

Mughniyeh has long been a target for Israel and America. He was responsible for bombing the US marine barracks and embassy in Beirut in 1983, in which more than 350 died, and was behind an attack on the Israeli embassy in Buenos Aires in 1992, which killed 29.

One source suggested the brothers may have been “spotters”, part of an observation team that monitored Mughniyeh’s movements shortly before his death. Others said there was no direct evidence of this. According to the Lebanese army, Jarrah and his brother were found to possess “communication devices and other sophisticated equipment”.

Lebanese investigators impounded a Mitsubishi Pajero 4x4 parked in front of Jarrah’s home. The vehicle was said to be fitted with advanced surveillance equipment.

“Some equipment was found in his house; other items were hidden in a vehicle,” said a security official who claimed the men had also been monitoring the movement of officials crossing the Syrian-Lebanese border.

According to Lebanese sources, the Jarrah brothers were recruited by Israel during the 1980s, when the Israeli army controlled large swathes of southern Lebanon.

Ali Jarrah is said to have joined militant Palestinian groups, which enabled him to travel between Lebanon and Syria and move around Damascus without attracting suspicion.

Sources close to the investigation said Jarrah had confessed to having been recruited by the Israelis to gather intelligence on militant Palestinian organisations in Lebanon.

Only in recent years had he started to monitor senior figures in Hezbollah, it was claimed. A statement issued by the Lebanese army said the two men had admitted to “gathering information on political party offices and monitoring the movements of party figures for the enemy”.

The Beirut paper As-Safir reported that during the war with Israel in southern Lebanon in 2006, Jarrah was seen with a video camera at relief centres connected to Hezbollah. “Was he pinpointing security targets in the Bekaa?” it asked.

According to the paper, investigators are attempting to determine whether a video camera fixed inside Jarrah’s car was directly connected by a satellite link to controllers in Israel.

Since the death of Mughniyeh, who was killed instantly when a booby-trapped headrest in his 4x4 exploded, Hezbollah has been determined to track down his assassins.

The brothers had apparently been frequent visitors to the Kfar Sousa district of Damascus where Mughniyeh, who had an American bounty of $5m (£3.2m) on his head, was finally identified.

According to some reports, Jarrah was first picked up in the southern suburbs of Beirut by Hezbollah security men on July 7, after being suspected of having had a role in Mughniyeh’s assassination.

Hezbollah is said to have finally handed Jarrah to the Lebanese authorities after questioning him for nearly four months.

According to Lebanese security sources, the brothers are distantly related to Ziad Jarrah, one of the hijackers of United Airlines Flight 93, which crashed into a Pennsylvania field on September 11, 2001, killing everyone on board. Their families come from the same town in the Bekaa valley.

The Israeli government has refused to comment on the arrests.

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