As Iranian ambassador to Syria from 1981 to 1985, he was instrumental in funding, arming and organising Hizbollah, the Islamic fundamentalist militia in Lebanon. Intelligence agencies investigating the 1983 suicide car bombings against US and French troops in Beirut concluded that the Iranian embassy in Damascus played a critical role in the operation.
I met Mohtashemi at the time, a quiet-spoken, courtly individual who made much of his clerical status and spoke Farsi and Arabic in a refined and diplomatic style. Only when talking of America or Israel did his serenity seem to desert him.
Mohtashemi and his staff were also building close alliances at this time with radical Palestinian groups, including the Popular Front for the Liberation of Palestine - General Command, which was later suspected of involvement in the Lockerbie bombing.
Syrian officials paid deference to Mohtashemi's radical sentiments but privately detested the Iranians, with whom they maintained a pragmatic alliance against US policy in Lebanon.
It was shortly afterwards that Mohtashemi himself became a victim of terrorism, when he opened a parcel in the embassy which exploded, blowing off one hand, several fingers and an ear. He left Syria, to the evident relief of his hosts, and returned to take up the post of Interior Minister in Iran.
He then became the most important Iranian official connected to Hizbollah, which staged a series of kidnappings and murders of Western hostages in Lebanon from 1985 to 1991. He was regarded by Washington as the man with greatest influence over the most violent pro-Iranian factions in Lebanon, a skilful clerical politician who employed the security services at his disposal to operate an extremist parallel foreign policy.
The Lockerbie bombing, which followed the downing of an Iranian civil airliner by the US Navy, was regarded by Islamic radicals as a classic operation. In the search for easy solutions that "blamed" Iran, Libya or Syria, Western analysts tended to neglect the simple fact that Mohtashemi and his allies had constructed a network of radical activists which transcended national borders, although it depended upon state support.
Mohtashemi lost the Interior Ministry in 1989 when President Rafsanjani took over, purged many of the radicals, solidified the peace with Iraq and wound down support for extremist groups abroad. Since then, he has contributed to Iran's thriving hardline newspapers, voiced criticism of Rafsanjani's policies in parliament and done his best to keep alive the flame of Khomeini's messianic ideology.