An early morning gun and bomb attack has shut down Iraq's biggest oil refinery, Baiji, with at least two employees killed.
The attackers stormed the site in Salaheddin province north of Baghdad at 0430 (0130 GMT), planting bombs in one of its units.
A fire broke out and the installation was badly damaged, officials said.
At one time the refinery was controlled by al-Qaeda, who used it to fund militants.
It is one of three major refineries in Iraq, the others being in the capital Baghdad and at Basra in the south.
Police said it took 50 fire engines to control the fire at the refinery, which processes about 150,000 barrels of oil per day.
"Armed men entered the refinery and shot dead two of the engineers," said Abdul Qader al-Saab, the facility's deputy chief.
"Then they detonated bombs at one unit, the al-Shamal unit, of the refinery, which represents 25 percent of the refinery's production. In the morning, we came to put out the fire, which erupted as a result of the bombs."
The governor of Salaheddin province, Ahmed al-Jubouri, said the refinery had "completely stopped".
"It's a big loss for the whole country. All Iraqi cities depend on its production," he told Reuters.
An unnamed official at the refinery said fixing the damage would take "a long time", saying the damage was "severe".
But he added that it was hoped a partial restart could be made "in the next few days".
The BBC's Jonathan Head in Baghdad says that militant attacks on strategic targets are a regular occurrence in Iraq, but the timing and target of this one will worry the government.
Inconsistent fuel supplies are one of the big complaints made by Iraqis about their living conditions, our correspondent says, and the attack comes a day after angry protests in several cities.
Meanwhile, in the southern town of Samawa, a second refinery was shut down by fire, but officials said initial reports indicated it was started by a technical failure rather than an attack, according to Reuters.