Kigali – At least 6 000 Burundian refugees have fled into Rwanda over the past month, Rwandan officials said, fearing violence in the build up to Burundi's presidential election.A dispute over whether President Pierre Nkurunziza can run for a third term - he has not yet announced any such plan - has triggered the worst political crisis since the 12-year civil war in the east African nation ended in 2005.Burundian refugees started crossing the border into Rwanda in mid-March but numbers have swelled in recent days, data from Rwanda's ministry of refugee affairs showed. At least 1 069 refugees arrived on Tuesday, taking the total to 5 954.Diplomats, activists and regional leaders have warned that tensions before the presidential poll could lead to unrest. Activists say Imbonerakure, the youth wing of Burundi's ruling party, often harass and even kill opposition members.The group has denied using violence and accused the opposition of trying to discredit it.ProtestOpposition parties and dissenting members within the ruling CNDD-FDD party say Nkurunziza running for a third term would violate a 2000 deal that ended the conflict between Hutu and Tutsi ethnic groups. Nkurunziza, in power since 2005, has not yet stated that he will run.Opposition groups and some dissenting CNDD-FDD party members said they planned to protest in the capital Bujumbura on Wednesday."US citizens should avoid these protests," the US state department said on Tuesday, although it added that recent protests in Bujumbura have been largely peaceful.Refugees at Rwanda's eastern Bugesera district, where most are housed in two transit centres, told Reuters last week that they fled fearing attacks from Imbonerakure.Rwanda's President Paul Kagame has raised the issue of refugees and the risk of violence when he met with Nkurunziza on Monday, the Rwandan presidency said in a statement.