By Prak Chan Thul
PHNOM PENH (Reuters) - Cambodian opposition leader Sam Rainsy returned home from exile on Friday after a royal pardon removed the threat of a jail term and he immediately joined the campaign to unseat long-serving Prime Minister Hun Sen in this month's election.
He received a rapturous welcome at Phnom Penh airport from tens of thousands of supporters, who stopped traffic, forcing some passengers to leave on foot with their luggage.
Later, addressing a huge crowd at Freedom Park in the capital, he thanked King Norodom Sihamoni for the pardon and said: "I have received my full freedom and will use this freedom to protect Cambodians in the whole country."
A former finance minister, Sam Rainsy was sentenced to 12 years in prison in absentia in 2010 on charges of spreading disinformation and falsifying maps to contest a new border agreed by Cambodia and Vietnam.
He had chosen exile the previous year rather than face trial for what U.S.-based Human Rights Watch said at the time were politically motivated charges that showed Hun Sen was "no longer interested in even the pretence of democracy".
In power for 28 years, Hun Sen seems likely to win election again with his Cambodian People's Party (CPP). But the opposition Cambodia National Rescue Party (CNRP), formed through a merger last year, including the Sam Rainsy Party, is mounting a strong campaign with a simple slogan: "Change".
"We must have absolute change, the change from being inferior to being a developed and civilized country," Sam Rainsy told supporters in the park.
He appealed for the votes of low-level government workers who feared they might lose their jobs if the government changed, saying they would not be dismissed but that a CNPR government would pursue more senior officials suspected of corruption.
Police said there had been scuffles between supporters of the two parties, but only minor injuries were reported.
Hun Sen has brought stability to Cambodia after decades of upheaval. That has attracted foreign investment, particularly in the garment sector, but he is seen as authoritarian by critics and brooks little dissent.
His request to King Norodom Sihamoni to pardon Sam Rainsy came as a surprise, but it may have been aimed at fending off criticism from the United States, European Union and others after allegations by his opponents of electoral misconduct.
In the letter carrying the request, read out on state television, he said this was based on "national reconciliation" and the fact that Sam Rainsy's return would ensure the July 28 election was democratic and free.
It is still not clear if Sam Rainsy will be able to contest a parliamentary seat, but he will galvanize the CNRP campaign around the country over the coming week.
"I came here just to see him, I miss him and I love him," Kong Oun, 66, said at the airport. "He is the cleanest person in the nation and the CNRP will win the election if there is no cheating."
Independent analyst Chea Vannath said the turnout on Friday proved that Sam Rainsy had huge support and the newly merged opposition could make gains in the election.
"The two parties are unified. That's what their supporters wanted and there is growing support among the youth," she said. "Sam Rainsy's return has made the support even stronger, this is a boost for the opposition party and that they will win more seats."
The Sam Rainsy Party had 26 of the 123 seats in the outgoing parliament and the newly merged party had 29 in total, with Hun Sen's CPP accounting for 90.
On June 8, after a CPP-dominated committee expelled the 29 opposition lawmakers from parliament, the U.S. State Department called for "a political process that includes the full participation of all political parties on a level playing field".
The parliamentary committee had said the 29 were not eligible to sit since the parties for which they were elected no longer existed.
(Editing by Alan Raybould and Ron Popeski)