From a 2002 article in Perceptions:

While Osama bin Laden may be the American governments most wanted terrorist, many present and former Central Intelligence Agency officials and counter terrorism specialists consider Imad Mughniyeh to be the most dangerous man alive. Who exactly is Mughniyeh? He was a founding member of Lebanese Hizbollah, and reportedly directed both Hizbollahs security wing and its overseas operations. However, Mughniyehs trail of blood has shown that Hizbollah is not merely some resistance army engaged in a struggle against Israel, as many of apologists like to assert. Mughniyeh is suspected of planning the suicide attacks against the US embassy in Beirut in 1983, as well as both the American and French marine barracks later that same year (by targeting the peacekeepers, Mughniyeh fulfilled Hizbollahs and their Iranian sponsors objective of prolonging the Lebanese civil war). Beginning in 1984, Mughniyeh masterminded a series of kidnappings of several Westerners and is alleged to have personally tortured and murdered William Buckley, the Central Intelligence Agency Station Chief in Beirut. In 1985, he participated in the hijacking to Beirut of a TWA passenger jet en route to Rome from Athens. During the course of the ensuing 17-day hostage seizure, the hijackers murdered an American passenger. In 1992, Mughniyeh planned the car bomb attack on the Israel embassy in Argentina. Lest any apologists claim that Hizbollahs struggle against Israel is merely political and therefore legitimate, Mughniyeh showed his true colours again in Buenos Aires in 1994, when he orchestrated the bomb attack on the Jewish cultural centre. Most recently, Mughniyeh’s name surfaced as the facilitator for a shipment of 50-tons of Iranian arms the Palestinian Authority ordered, but which the Israeli military intercepted in the Red Sea. Janes Intelligence Review reported that Israeli military intelligence analysts still consider Mughniyeh to be the mastermind of the World Trade Centre attacks.

And confirmation from the Iranian press.