The Islamic State jihadist group launched a fresh offensive Thursday against Iraq's largest refinery, where a military official said security forces are facing one of their toughest battles.
The IS launched "a fierce attack at dawn and clashes are ongoing," an army major general told AFP, on condition of anonymity because he is not authorised to talk to the press.
The country's largest refinery is located near the city of Baiji, around 200 kilometres (120 miles) north of Baghdad.
Following a victory against jihadist fighters in Tikrit, government and allied forces have vowed to continue working their way north. Control of the Baiji area is seen as key step toward the reconquest of the main IS hub of Mosul.
"The battle for Baiji refinery is a real test for the Iraqi forces and it's one of the most complicated battles we have," the major general said.
The vast refinery complex remained besieged by IS fighters for months following the group's massive onslaught across Iraq in June 2014.
The siege was broken last year but IS attacked anew and in April some of its fighters managed to establish a foothold inside the refinery compound.
"The terrorists who broke in three weeks ago are taking positions in buildings. They are suicide fighters who will not leave until they have been killed," the officer said.
"Our security forces are struggling to go after them, they are inside buildings, next to pipes and tanks and setting them on fire," he said.
He said army, police, counter-terrorism forces and several Shia militias fighting under the umbrella of the volunteer Popular Mobilisation units were involved in the fight.
IS said in its daily radio broadcast Thursday that its fighters had carried out two suicide attacks on Wednesday, one using a truck inside the refinery complex and another using a military vehicle outside the compound perimeter.
According to the US-led international coalition fighting IS in Iraq and Syria, 22 coalition air strikes have been carried out in the Baiji area this month alone.