Iraq’s crude oil shipments to the United States have fallen to the second lowest monthly level in almost four years, the U.S. Energy Department has confirmed. Iraq exported 341,000 barrels of crude oil a day that month to the U.S. market in May, down 39 percent from the month before.

The Energy Department said it was Iraq’s second smallest volume of crude sent to the United States since September 2003, a few months after American forces removed Saddam Hussein from power.

The United States imported an average 553,000 barrels of oil a day last year from Iraq, making it America’s sixth largest foreign oil supplier. But shipments are down so far this year as Iraq’s oil sector has been hit by insurgent attacks, disrupting oil production and exports.

Iraq’s oil production averages about 2.1 million barrels a day, down from daily output of 2.5 million barrels before the war and much less than the 3 million barrels a day the Bush administration had hoped Iraq would be pumping by now.