PORT HARCOURT, Nigeria, April 4 (Reuters) - Nigeria's delta region was hit by violence on Friday, as gunmen killed nine people and, separately, militants blew up a gas pipeline, in a sign of returning unrest to the oil producing area days after a relatively peaceful presidential election.
Opposition presidential candidate Muhammadu Buhari beat incumbent Goodluck Jonathan in a landslide victory last weekend, producing some resentment in Jonathan's home region.
On Friday evening, in the town of Obrikom and the nearby village of Obor in Rivers state, gunmen went on a shooting spree, the police said.
"Some unknown armed men invaded the Obrikom and Obor communities ... killing nine, injuring two persons," Rivers state police spokesman Ahmed Mohammad said on Saturday.
The house of a parliamentary opposition candidate, Vincent Ogbagu of Buhari's All Progressives Congress, was set on fire.
Rivers, the home of oil and gas in Africa's biggest crude producer, was expected to be a flashpoint for election-related violence, particularly due to tensions between Governor Chibuike Amaechi and the presidency after he defected to the APC.
Gunfire and explosions hit an opposition rally in February, wounding several people, and other non-fatal bomb blasts rocked the state ahead of the polls.
On election day, at least two people were killed, including a member of the military, but tensions were deflated after Jonathan's early acceptance of defeat and call for calm.
In Delta state, militants from the Urhobo ethnic minority group blew up a gas pipeline in the early hours of Friday to draw attention to their exclusion from lucrative pipeline protection contracts with the state oil company, an official said.
"The Urhobo militants who carried out the attack have claimed responsibility," said Isa Ado, spokesman for the Pulo Shield taskforce, made up of members of various Nigerian security forces.
Reuters was not able to immediately contact the Urhobo group for comment.
Some former militants of the Movement for the Emancipation of the Niger Delta, which wrought havoc in the oil-producing creeks in the early 2000s, threatened to take up arms again should Jonathan lose but there was no immediate backlash after the president accepted defeat.
His People's Democratic Party swept the vote in Rivers and neighboring Bayelsa and Delta states.
The APC said the election had barely taken place in much of Rivers state and was a sham. The electoral commission sent a team to investigate but ultimately kept the results.
Observers said the Rivers vote was marred by ill-equipped polling units, unprepared electoral officers and some violence. (Additional reporting by Tife Owolabi in Yenagoa, Writing by Julia Payne; Editing by Robin Pomeroy)