It was unclear whether there was any political motive behind the killing of the diplomat, Fred Woodruff, who authorities said was hit by a single bullet fired through the windscreen of the four-wheel-drive Russian Niva vehicle.
US authorities said that Mr Woodruff, 45, was a regional-affairs officer on temporary duty at the US embassy in Tbilisi, who was due to return home later this month.
The US State Department in Washington yesterday said that it regretted the 'awful incident' but declined to speculate on the motive for the attack until the outcome of a joint US-Georgian investigation.
The incident is a blow for Mr Shevardnadze, as it comes at a time when he has been seeking support from the United States in reviving Georgia's economy.
It also coincides with plans by Washington to step up its efforts to help to broker an end to ethnic and religious disputes in the former Soviet Union, which threaten to destabilise the Russian President, Boris Yeltsin.
For months Georgia has been ravaged by the effects of severe internal strife, including a civil war with separatist rebels from the western province of Abkhazia.
Last month the Secretary-General of the United Nations, Boutros Boutros-Ghali, said that 50 military observers should be sent to Georgia in an attempt to help bring the conflict under control.
Georgia's prosecutor-general is leading an investigation into Mr Woodruff's death, which happened after dark at around 9.30pm on Sunday in an area often patrolled by groups of armed men. A spokesman for the Interior Ministry said Mr Woodruff was returning to Tbilisi after a sightseeing trip to the country.
Mr Shevardnadze's chief of personal security, Eldar Gugusladze, escaped unhurt in the attack, which happened in a village about 15 miles outside the capital.
Whether he rather than the diplomat was the intended target, or whether the gunmen believed that the Georgian leader was in the car, remained uncertain last night.
The Georgian authorities issued a statement expressing 'deep sorrow' over a 'tragic and senseless incident' and praising Mr Woodruff, a Soviet- affairs expert, for serving 'the noble cause of developing relations between the two countries'.
During a radio broadcast Mr Shevardnadze referred to Mr Woodruff's death as a murder, indicating that he thought it was the work of 'mafioso structures and criminal elements'.
The Georgian leader said that the killing demonstrated the need to curb violence in the country, which has been plagued by armed criminal gangs and random street violence. The unrest is such that Mr Shevardnadze, the former Soviet foreign minister, is reported to be considering imposing a state of emergency.
'Order must be restored in the country,' Mr Shevardnadze said. 'This is today's most important task . . . even if we must temporarily restrict our democratic achievements to save democracy.'Reuse content