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.
"I come to rescue the nation with you, brothers, sisters and nephews," Sam Rainsy, speaking through a microphone on the back of a pickup truck, told thousands of supporters lining the road from Phnom Penh airport.
The crowds brought traffic to a halt and forced some passengers to leave the airport on foot with their luggage.
Sam Rainsy, a former finance minister, 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 retain power 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.
Hun Sen asked King Norodom Sihamoni to pardon Sam Rainsy this month, a move that 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, which has been 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 lead the CNRP campaign around the country over the coming week.
The CNRP said between 30,000 and 40,000 people, including Buddhist monks, had turned out to welcome him back. Thousands more were joining the crowd as it moved towards the centre of town, following his vehicle.
Supporters with stickers bearing the party's "rising sun" logo on their cheeks chanted" "Change, change!"
"I came here just to see him, I miss him and I love him," said Kong Oun, 66, who had travelled from Prey Veng province in the southeast. "He is the cleanest person in the nation and the CNRP will win the election if there is no cheating."
On June 8, after a CPP-dominated committee had expelled 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)