Investigators questioned two soldiers Wednesday over the kidnapping of Chelsea footballer John Obi Mikel's father, freed this week in a Nigerian police raid, the military said.

Describing his kidnapping to journalists after being freed on Monday, Michael Obi said he had been thrown into a van painted in military colours and beaten by men in military garb. It was not clear whether they were legitimate soldiers.

Police announced the arrest of six people following Monday's raid in the northern city of Kano, hundreds of kilometres from where the August 12 abduction took place in Jos. None of the six were members of the army.

But police later said two soldiers were suspected of involvement, and the military confirmed Wednesday that they were being questioned.

"We are carrying out investigations," Lieutenant Colonel Andrew Idachaba, a military spokesman in Plateau state, told AFP.

"We want to ascertain the level of their involvement in the kidnap. We want to authenticate whether they are actually involved ... The two soldiers are being interrogated by the military police and the (army) intelligence unit."

Plateau state police commissioner Emmanuel Dipo Ayeni told journalists that "two of the soldiers that kidnapped Michael Obi have been identified."

No ransom was paid to free Obi, according to police, who said they raided a house in Kano where he was being held after receiving information from a suspect.

Obi said the kidnappers had demanded a ransom of 10 million naira ($64,000, 45,000 euros).