At least 40 people have been killed in mutiple attacks in northern and southern Nigeria.

The majority of the victims died when explosions ripped through a joint civilian and military checkpoint in Biu, in Borno State, on Tuesday.

Elsewhere, an attack on an opposition rally in Okrika, in Rivers State, left one policeman dead and several others wounded, while a reporter covering the event was stabbed.

Five explosions and a burst of gunfire hit the rally of Dakuku Peterside, the All Progressive Congress (APC) candidate for governor, with his supporters running for safety.

"Five police officers were shot. One of them is dead and four are lying in critical condition at this hospital," Peterside said.



Peterside and a source at the private Channels television network said its reporter at the scene, Charles Erukaa, had also been stabbed and was being taken to a hospital.

Political tension has raged in Rivers since outgoing governor Rotimi Amaechi defected to the APC from the ruling Peoples Democratic Party (PDP) in 2013.

Suicide attack

In Potiskum, in the northeasternn state of Yobe, three people were killed on Tuesday in a suicide blast.

A bomber blew himself up inside al-Amir restaurant, killing the manager and a steward, officials told the AFP news agency. Thirteen staff and customers were seriously injured.

"We evacuated three dead bodies which included the bomber and two victims to the hospital," said a police officer involved in the rescue operation.

Meanwhile, the death toll increased to 36 people after an attack in neighbouring Borno State, near the town of Biu, where at least three explosions struck a joint civilian and military checkpoint, witnesses and vigilantes said.

"Most of the victims were child vendors and beggars that usually crowd the checkpoint to sell wares and beg for alms," a medical source at Biu General Hospital told AFP.

Gana Sheriff, a vigilante, said the attack happened at Yamarkumi village, four kilometres from Biu in Borno state.

"It was a suicide attack by three men in a motorised tricycle," Sheriff said.

"It was later that we realised the attackers came in two rickshaws. The one ahead had three people inside who opened fire and detonated three explosives.

"The second rickshaw immediately turned after the explosions but was pursued into the bush by soldiers and local hunters."

Biu is a local government area to the south of Borno, which has been the site of previous attacks by the armed group Boko Haram.

Boko Haram was cited as a reason for postponing Nigeria's election by six weeks which had been due to take place on Saturday.