Libya had sought to improve relations with the US under the presidency of Jimmy Carter, for instance by courting his brother, the businessman Billy Carter, but in 1979 the US placed Libya on its list of "State Sponsors of Terrorism". Relations were further damaged at the end of the year when a demonstration torched the US embassy in Tripoli in solidarity with the perpetrators of the Iran hostage crisis. The following year, Libyan fighters began intercepting US fighter jets flying over the Mediterranean, signalling the collapse of relations between the two countries. Major sources in the Italian media have alleged that the Itavia Flight 870 was shot down during a dogfight involving Libyan, United States, French and Italian Air Force fighters in an assassination attempt by NATO members on an important Libyan politician, perhaps even Gaddafi, who was flying in the same airspace that evening. Libyan relations with Lebanon and Shi'ite communities across the world also deteriorated due to the August 1978 disappearance of imam Musa al-Sadr when visiting Libya; the Lebanese accused Gaddafi of having him killed or imprisoned, a charge he denied. Relations with Syria improved, as Gaddafi and Syrian President Hafez al-Assad shared an enmity with Israel and Egypt's Sadat. In 1980, they proposed a political union, with Libya promising to pay off Syria's £1-billion debt to the Soviet Union; although pressures led Assad to pull out, they remained allies. Another key ally was Uganda, and in 1979, Gaddafi sent 2,500 troops into Uganda to defend the regime of President Idi Amin from Tanzanian invaders. The mission failed; 400 Libyans were killed and they were forced to retreat. Gaddafi later came to regret his alliance with Amin, openly criticizing him as a "fascist" and a "show-off".