Niger Delta rebels had warned that bombs have been planted at the venue of Friday's anniversary parade [AFP]

South African police have arrested and are questioning the alleged leader of the main militant group in the Niger Delta in connection with attacks in Nigeria during independence celebrations.

According to members of the group, the Movement for the Emancipation of the Niger Delta (MEND), suspected leader Henry Okah was arrested at his Johannesburg home on Saturday.

Al Jazeera's Yvonne Ndege, reporting from Nigeria's capital Abuja, said it was still unclear what charges Okah might face.

"We know that he is being interrogated by security agents in South Africa, and that this comes as no surprise ... on Thursday, Henry's Okah's house in South Africa was raided by operatives from Interpol," Ndege said.

"And the allegation then was that he was plotting to bomb Abuja on Independence Day. Of course, this actually happened on Friday."

The attacks came as President Goodluck Jonathan and other dignitaries sat at a celebration only a 10-minute walk away, however, Jonathan said on Saturday that "terrorists" and not MEND were behind the two car bombings near independence day celebrations.

At least 12 people were killed and another 17 wounded in the two explosions in Abuja as the country marked its 50th independence anniversary.

The explosives detonated on the parade grounds surrounding Eagle Square in the capital. A third, smaller explosion hit still closer to the square, where Nigeria's president stood with other dignitaries, injuring one person.

Bomb threat

Earlier on Friday, rebels from the oil-producing south threatened to bomb celebrations in the city. In an email, fighters from the Niger delta said bombs had been planted at the venue of Friday's lavish parade attended by senior officials and foreign dignitaries.

"Several explosive devices have been successfully planted in and around the venue by our operatives working inside the government security services," the email, signed by Jomo Gbomo, said.

The message urged people to evacuate by 09:30 GMT.

"In evacuating the area, keep a safe distance from vehicles and trash bins."

However, television footage of the parade at the time the deadline expired showed no reaction by security forces.

Ayo Johnson, an African specialist, spoke to Al Jazeera and said that the attackers seem to have backing from inside the security forces.

"The act shows that the security forces on the ground have not been effective because they could have protected the area better.

"This also shows that the perpetrators are getting backing, because they were able to get through the security forces with the president and all the dignitaries there.

"It is a rather embarrassing concern for the government," he said.

The president attended the parade dressed in his traditional black fedora hat and dark suit, before inspecting massed ranks of soldiers on the rain-swept parade ground from an open-top jeep.

He is from the Niger delta area and analysts have expressed the view that rebels from the same region would not want to cause him serious embarrassment.

MEND has battled the central government for years in a bid to obtain a greater share of federal oil revenues for the impoverished Niger Delta region.

Source: Al Jazeera and agencies