PORT HARCOURT, Nigeria, Jan 7 (Reuters) - Nigeria's two main political parties traded blame on Tuesday over a small bomb blast at a court in oil-producing Rivers state a day earlier, a signal of the growing risk of violence ahead of elections next year.
The improvised device went off early on Monday in the High Court in Ahaoda, causing some damage but no casualties, state police spokesman Ahmad Mohammad said.
Rivers, like much of the Niger Delta, has a history of instability, gangsterism and political thuggishness that tends to worsen in the build up to elections as rival factions jockey for power.
The 2015 national poll is expected to be the most closely fought since the end of military rule 15 years ago because of a row within President Goodluck Jonathan's ruling People's Democratic Party (PDP) over his assumed intention to run for another term, and because the opposition coalition is more powerful and has broader national appeal than any previous one.
Rivers Governor Rotimi Amaechi last year defected from Jonathan's PDP, intensifying a row between them.
Amaechi joined the main opposition All Progressives Congress (APC), giving the newly formed opposition coalition a foothold in Jonathan's home Niger Delta region and heightening the rivalries that often lead to violence in Africa's second largest economy.
The PDP and APC both said they suspected the other side of sabotaging the court, which was due to hear a case over the disputed leadership in the state national assembly.
Rivers is the largest state in the Delta, where the bulk of Nigeria's 2 million barrel per day of crude oil is produced and it exports the world's fourth largest quantity of liquefied natural gas (LNG).
Both oil and LNG exports have been hampered by sabotage and theft attacks on pipelines. Large scale oil theft is worth billions of dollars a year and industry experts believe the scale of the problem means high-level politicians are involved.
The oil-producing delta is far from the reach of the Islamist militant group Boko Haram, which mostly carries out its attacks on security forces, churches and schools in the mainly Muslim north of Africa's most populous nation. (Reporting by Jackson Ohamege; Writing by Joe Brock; Editing by Tim Cocks and Alison Williams)