The Nigerian government has fined British Airways $135m (£86m) and Virgin Atlantic $100m (£63m) over what it says are unfair trade practices, an official says.

The fines came after a six-month investigation into ticket prices from Lagos's Murtala Muhammed International Airport to London's Heathrow Airport.

The official, who asked not to be named, said the carriers levied unreasonable fuel surplus prices on consumers.

The fines come as Nigeria is in talks with the UK over a Nigerian carrier losing spots at Heathrow. The Nigerian official denied the fines came as a response to the dispute with the UK over Heathrow slots, which has seen the Nigerian government threaten to cut British Airways flights in Lagos in retaliation.

The official said the two airlines acted together to inflate prices as far back as 2004. Nigerian newspaper ThisDay published a story saying the government had levied the heavy fines.

Virgin Atlantic Airways issued a statement saying it "has received correspondence from the Nigerian Civil Aviation Authority relating to an inquiry surrounding historic passenger fuel surcharges.

"We have fully assisted the NCAA with its inquiry and we do not believe we have breached Nigerian law," the statement read. "We will be robustly defending any suggestion to the contrary."

The airlines will also be required to provide compensation for affected passengers, which could mean millions of dollars more in losses, the official said.

Later, BA said: "We reject the allegations made by the Nigerian Civil Aviation Authority and we are vigorously defending our position.

"We remain committed to Nigeria and have been flying there for more than 75 years. We pride ourselves on offering competitive fares, a choice of products and connections to our Nigerian customers."