IATA says $1 billion of revenue belonging to foreign airlines is being withheld across Africa, although Nigeria is the only country where the value of blocked funds has risen.

The $450 million, the largest amount withheld by any African nation, in May was 12.5% higher than the previous month.

Algeria, Ethiopia and Zimbabwe, who combined are withholding $271 million from foreign airlines, in May marginally paid down what they owed. Eritrea was unchanged at $75 million, IATA said.