Foreign private security personnel from Russia, South Africa and South Korea were training the Nigerian army but not being deployed to the front line, the Nigerian government said on Tuesday (17 March).
A number of reports have emerged in recent days, which suggested foreign mercenaries were directly involved in fighting the Islamist militant group Boko Haram.
The Nigerian government said that any foreigners on the ground in north-east Nigeria (a Boko Haram stronghold in the country) were there to train military troops rather than engage in fighting the militants directly.
"There are trainers on the ground to assist in the handling of equipment," Mike Omeri, a government spokesman, told Reuters news agency. "They simulate, they teach. These are the things they do."
When asked if the foreigners were involved in fighting directly, Omeri said "I am not aware of that."
"This is training on site and maybe this is why the people on the ground have been described as mercenaries," Omeri said.
Africa's biggest economy and most populous nation is due to hold elections on 28 March. The vote was due to take place on 14 February but was delayed by the government over security concerns.
Boko Haram has sought to establish an Islamic state in north-east Nigeria since 2009. The group has come under attack in recent months from both the Nigerian army and a number of regional allies, concerned that it could expand its attacks outside of Nigeria.