Iraqi oil exports rose in January compared to the previous month but revenue fell by more than $650 million due to plunging crude prices, the oil ministry said on Monday.

Baghdad is facing a financial crisis due to the fall in oil prices, which the ministry said averaged $22.21 in January -- less than half the amount projected in the 2016 budget.

Iraq exported an average of 3.28 million barrels per day in January, up from 3.21 million in December, but monthly revenue fell from $2.92 billion to $2.26 billion, the ministry said in a statement.

The decrease was due to the fall in oil prices, which averaged around $29 in December.

Neither month included oil exports from northern Iraq through the Turkish port of Ceyhan, the ministry said.

That is because Iraq's autonomous Kurdish region has been independently exporting oil from four northern provinces since a deal between it and the federal government collapsed last year.

Finance Minister Hoshyar Zebari has warned that 2016 "will be a difficult and harsh year" for Iraq, and that "projections indicate a continued collapse of oil prices."

Iraq can ill afford the drop in oil revenue, which it relies on for the vast majority of government funds, at a time when it is fighting a costly war against the Islamic State jihadist group, which overran large areas of the country in 2014.

Millions of Iraqis have been displaced by violence and hundreds of thousands more are expected to flee fighting in 2016.

And areas that are retaken from the jihadists are often devastated by the fighting and will cost a huge amount to rebuild.

On Sunday, the United Nations appealed for $861 million in humanitarian aid for Iraq to help plug the estimated $891 million gap between planned Iraqi expenditures on relief operations and available government funds.

"The government has its back against the wall because the price of oil is so low, and that's why we're asking the international community to be generous," said Lise Grande, the UN humanitarian coordinator for the country.