His presence in the Syrian capital, however, places the Syrian government of President Bashar Assad in an embarrassing position, given the fact that Mughnieh was wanted by Interpol and by the United States.

Following an initial honeymoon period which saw close cooperation between Syrian and U.S. intelligence services in the aftermath of the Sept. 11, 2001 terrorist attacks on the World Trade Center and the Pentagon, relations between Damascus and Washington worsened with the Bush administration accusing the Syrians of supporting anti-coalition forces in Iraq.

Furthermore, Washington has accused Damascus of giving assistance to groups considered to engage in terrorist activities. Damascus, however, has long denied its involvement in supporting terrorist activities aimed at destabilizing U.S. and Western interests, and refuted claims that one of the world's most wanted terrorists was given refuge in Syria.

Mughnieh's death in the Syrian capital Tuesday will no doubt be difficult for Damascus to explain, placing the government in front of a political dilemma. If Damascus acknowledges his presence it justifies claims by the United States and Israel of Syria's involvement with terrorist organizations. On the other hand, a denial by Damascus of any knowledge of Mughnieh's presence on its territory – a distinct possibility – would be awkward for Syrian intelligence services. That would be perceived as a gross lapse for a service reputed to maintain tight control on activities on its territory.

The accusations against Mughnieh are impressive. U.S. intelligence believes him responsible for killing 241 American military service personnel in 1983, in what was then described as the largest non-nuclear explosion, when a truck loaded with explosives blew up a building housing U.S. Marines stationed in Beirut as part of the multinational peacekeeping force.

U.S. intelligence services also believe Mughnieh to have masterminded the attack which destroyed the U.S. Embassy in Beirut. The Beirut Embassy bombing occurred while a high-level meeting of CIA operatives in the Middle East was underway. Their deaths were a devastating blow to U.S. intelligence gathering efforts in the Middle East and created a huge void in tracking terrorist activities for several years.

The United States also believes he was responsible for the abduction of Beirut CIA chief William Buckley. Buckley is believed to have been kidnapped by Mughnieh in the Lebanese capital and transferred to Tehran, where he died under torture.

He is also believed to have organized the hijacking of a TWA airliner in Beirut in which a U.S. navy diver was killed and his body thrown onto the tarmac.

Mughnieh was on the Interpol wanted list for his alleged participation in an attack on an Israeli-Argentine target in which 85 people were killed and close to 300 wounded.

One of the most wanted men in the world, and sought by several Western and Israeli intelligence agencies, Mughnieh remained in hiding since the end of the 1980s, when he was linked to the abductions of a number of Westerners during Lebanon's 1975-1990 civil war. He is believed to have undergone a number of identity changes, including plastic surgeries, in order to avoid being recognized or captured.

Mughnieh was reported to be responsible for a special unit of Hezbollah that was particularly active in the 1980s and 90s. Israel linked him to the 1992 bombing of the Israeli Embassy in Buenos Aires which killed 29 people.

It is widely believed by a number of Western intelligence sources that Mughnieh worked closely with Iranian intelligence services and he was thought to be hiding in the Iranian capital.

Hezbollah, who in recent years tried to distance itself from Mughnieh and his activities, described him as a "A great jihadi [holy fighter] of the Islamic Resistance in Lebanon [Hezbollah]." Al-Manar, Hezbollah's television channel issued a statement saying: "The leader Imad Mughnieh died a martyr, assassinated by the Zionist Israelis." Senior Shiite cleric Sayyed Muhammad Hussein Fadlallah issued a statement saying that "the resistance [Hezbollah] has lost one of its pillars."

While no one is likely to claim responsibility for Mughnieh's killing in Damascus, many will question his presence in the Syrian capital.