A government spokesman confirmed at least one death. But local independent TV station WBS reported that five had died when police opened fire on opposition supporters who threw stones at the cars. The vehicles included a convoy carrying Nigerian President Goodluck Jonathan.
Police were unavailable for comment on the TV report.
Museveni, who has held power for 25 years, was sworn in for a fourth term on Thursday after winning elections in February that opposition parties said were rigged. Since the vote, opposition leaders including Kizza Besigye have led a series of often violent protests against high food and fuel prices.
On Thursday, Besigye’s supporters also clashed with police as the crowd escorted him from Entebbe airport into Kampala.
Police said they had to move in after crowds started throwing stones at vehicles carrying guests at the inauguration.
“President Goodluck Jonathan of Nigeria’s convoy was attacked by Dr Besigye’s supporters as it was heading to Entebbe State House for the luncheon with the President,” said Fred Opolot, director of the government media centre.
“Unfortunately, a (motorcyclist) who was crossing (near) the president’s car was shot dead. The security forces mostly used rubber bullets. But he really posed a threat to a foreign dignitary who happened to be a head of state.”
Besigye has been arrested four times since protests began in April. He was returning to Uganda from Kenya, where he had received hospital treatment for injuries suffered during his last arrest, his supporters said.
Police spokeswoman Judith Nabakoba said crowds threw stones and pulled mirrors from the cars ferrying the dignitaries.
A Reuters witness said police doused the crowd in tear gas and beat them with sticks, blocking them from entering Kampala where they said they planned to hold a prayer meeting.
Earlier in the day, Besigye and his wife Winnie waved to several thousand ululating supporters through the sun-roof of their car. The crowds made V-for-victory signs amid a heavy security presence along the 40 km road leading to Kampala, where the inauguration was taking place.
During the ceremony, a different, jubilant crowd cheered as Museveni, sporting his trademark rancher’s hat, was sworn in, flanked by the leaders of Nigeria, Kenya, Zimbabwe, Tanzania, Ethiopia, Democratic Republic of Congo, Somalia and South Sudan.
In his speech, Museveni said food prices would come down following an expected bumper harvest, and accused others of being desperate for power and resorting to “disruptive schemes”. “Those disruptive schemes will be defeated,” he said.
Analysts say Museveni has picked a fight with Besigye, confident that donors will not criticise his tactics too much because Ugandan troops form the backbone of an African peacekeeping force in Somalia.
“Museveni knows that, as unpalatable as the actions of his regime may be, the donor states cannot afford to turn on him as long as he spares them having to deal with Somalia themselves,” said J. Peter Pham, Africa analyst at the Atlantic Council.
Other regional experts said Museveni, widely regarded as an astute political leader, would be wary of alarming foreign investors developing the east African country’s oil reserves.
Uganda struck oil on its western border with Congo in 2006 and commercial production is expected in 2012, bringing a flow of cash that Museveni promised will be used to transform his poverty-stricken country to a middle-income state by 2016.
Besigye was Museveni’s doctor during the guerrilla war that swept the rebel leader to power in 1986, but the two fell out and have been rivals ever since. Reuters