* Senior opposition figure missing ahead of vote
* Rights groups concerned about political environment
By Hereward Holland
KIGALI, July 13 (Reuters) - A senior Rwandan opposition official has gone missing after his car was found abandoned near the southern city of Butare, his party said on Tuesday.
Rights groups have accused the government of tightening the screws ahead of a presidential election in August. Two opposition leaders have been arrested in the runup to the vote.
Rwanda rejects accusations of clamping down on opponents and says the government has pursued dialogue and accepted opposing views since the 1994 genocide.
Democratic Green Party, which has been unable to gain registration and take part in the vote, said its vice-president, Andre Kagwa Rwisereka, went missing early on Tuesday and that his car had been found near the Mukula river.
"There’s no blood or anything, so we don’t know what actually happened... but it is confirmed that he is missing," the party’s president, Frank Habineza, told Reuters by telephone from Butare.
"His passport is inside the house. His national ID, driving permit and house keys were found inside the car, which indicates to us that he has not escaped the country."
Police confirmed Rwisereka’s pick-up truck had been found. "We are still following things to see if he fled or find out what happened," said police spokesman Eric Kayiranga.
Rights groups have expressed concern in past weeks about the increasingly repressive environment ahead of the election.
They say the arrest of two opposition leaders, the suspension of two newspapers and the murder of a critical journalist are signs of an increasing clampdown.
Incumbent President Paul Kagame, who has been praised for rebuilding the country as de facto leader since the 1994 genocide, is expected to win by a large margin, having secured over 90 percent of the votes in 2003.
Police have also arrested two journalists for articles that they said could rekindle ethnic hatred and incite public disorder. Authorities say strict anti-genocide legislation is necessary to avoid a repeat of the bloodshed 16 years ago. (Editing by George Obulutsa and Maria Golovnina)