Uganda: Yoweri Museveni sworn in as Besigye returns
Supporters of Uganda's opposition leader have clashed with police in the capital Kampala following the swearing-in of President Yoweri Museveni.
The Ugandan government says Kizza Besigye's supporters stoned convoys carrying dignitaries.
A spokesman said the Nigerian president's car had come under attack.
The spokesman added that one of Dr Besigye's supporters who came too near to a presidential convoy had been shot dead.
The government said it was part of a deliberate effort by Dr Besigye's Forum for Democratic Change party to undermine the government.
Mr Museveni, who has been in power since 1986, was sworn in for a fourth term as president as thousands of opposition supporters turned out to welcome Dr Besigye home from neighbouring Kenya.
Government spokesman Fred Opolot said the police had urged Dr Besigye to speed up his journey from Entebbe airport to the capital, Kampala, but he had defied them.
Dr Besigye and his wife, waving to the crowds from an open-top car, spent six hours driving the 40km (25 miles) from Entebbe airport to Kampala through crowds of cheering supporters.
As the supporters approached the city centre, six hours after setting off, military police began shooting in the air to disperse the crowds and tear gas was fired.
"The Nigerian president's car - stones were directed towards it; fortunately they were able to speed away," Mr Opolot told the BBC's Focus on Africa.
"Dr Besigye and his crowd were determined to embarrass President Museveni on his swearing-in day.
"Had the police taken action against the crowd, and particularly against Kizza Besigye, the police would have been condemned by the wider public, so it's a catch-22 situation.
"It is embarrassing for us, it's an image that we do not want the world to see of Uganda - what has happened is unfortunate and we really do apologise."
Dr Besigye, a former ally of Mr Museveni, sought medical treatment in Nairobi after being injured when he was arrested over anti-government protests.
The police have been accused of using excessive force to break up opposition protests in recent weeks, leading to at least nine deaths, according to Human Rights Watch.
Dr Besigye had been due to return from Kenya on Wednesday, but says he was prevented from doing so - this was denied by Uganda's authorities.
Mr Museveni took the oath of office at a ceremony at an airstrip in central Kampala, in front of thousands of supporters and the leaders of African countries including Kenya, Tanzania and Zimbabwe.
The ceremony was followed by a 21-gun salute.
The president boasted of his achievements and vowed to "defeat disrupting schemes" - seen as a reference to the opposition.
Dr Besigye says he was cheated in February's election, although he mustered only half as many votes as Mr Museveni.
The opposition has since been involved in "walk-to-work" protests over the rises in the cost of food and fuel.
The government accuses Dr Besigye of trying to organise an Egypt-style uprising. He has been arrested four times.
Mr Museveni was once seen as part of a new generation of African leaders, replacing the post-independence "Big Men".
But the treatment of Dr Besigye means Mr Museveni's commitment to democracy has now been questioned and some aid to Uganda has been cut.