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PHNOM PENH (Reuters) - Cambodia’s main opposition party chose acting leader Kem Sokha as its new president on Thursday after exiled leader Sam Rainsy resigned unexpectedly in the face of a possible ban ahead of elections.

Political tension has been increasing as opponents of Prime Minister Hun Sen, a former Khmer Rouge guerrilla, accuse him of unfair maneuvering to maintain his grip on power in local elections in June and a general election next year.

Speaking to hundreds of supporters after the party vote, Kem Sokha said the Cambodia National Rescue Party (CNRP) would improve public services by replacing commune chiefs from the ruling Cambodian People’s Party (CPP) at polls on June 4.

Hun Sen sent a letter to congratulate Kem Sokha, wishing him “good health and happiness in the family”.

Last month, Hun Sen’s ruling party parliamentarians amended a law to make it easier for the government to dissolve political parties. It bans anyone who has been convicted of an offense from leading a party.

Sam Rainsy has been convicted of a series of defamation charges and has lived in France since 2015 to avoid them. He rejects the charges as politically motivated, but said he was resigning to protect the party from being dissolved.

At the CNRP Congress, three other members of parliament were chosen as deputy leaders - Pol Ham, Mu Sochua and Eng Chhay Eang.

Kem Sokha promised an extra $500,000 for every commune if the party wins the 2018 election. He said its local representatives would not sign off on concessions that hurt local communities and would solve land disputes - major issues in rural Cambodia.

Hun Sen has said an opposition victory could lead to the return of civil war.