The Islamic State extremist group Tuesday made major advances inside one of Iraq's largest oil refinery complexes and killed the commander of its garrison.
The jihadists also seized petrol and crude oil tanks, a security official, speaking on condition of anonymity, told dpa.
The Baiji refinery,about 200 kilometres north of Baghdad, accounts for almost a third of Iraq's refinery capacity. It has been out of action since last year, when it was the scene of intense fighting.
Illegal oil sales from small refineries, mainly in neighbouring Syria, have been a key source of funding for Islamic State.
The developments show that the jihadists are still a formidable force in the area, despite the government's much-vaunted recapture of the city of Tikrit, 40 kilometres to the south.
The commander of government forces at the refinery, General Daif Ayyub, and nine of his bodyguards were killed in the attack, which began Monday when the militants overran the complex's outer defences.
Baiji is the most northerly outpost of government forces on the route between Baghdad and Iraq's second city, Mosul.
The recapture of Tikrit by government forces two weeks ago, after a month-long campaign, was seen as the first step ahead of the much more challenging task of recapturing Mosul.
The jihadists have held large areas of Sunni-dominated northern and western Iraq since they launched a lightning offensive last summer that saw government forces collapse and flee.
Meanwhile, Prime Minister Haider al-Abadi arrived in Washington where he is expected to seek further support, including arms supplies, from US President Barack Obama.
The US leads an international coalition that is engaged in an air campaign against the jihadists in Iraq and neighbouring Syria.
The coalition has provided key backing to Iraqi security forces and the Peshmerga troops of the autonomous Kurdistan region as they seek to roll back the jihadists' gains.
While an offensive on Mosul is not expected for months, the government has signalled its intent to launch a major campaign soon in the Sunni-dominated province of al-Anbar, which stretches west from Baghdad to the Syrian and Jordanian borders.
The United States has, however, objected to the role played in previous government offensives by Shiite militias, which are backed by neighbouring Iran and have been accused of atrocities against Sunni civilians.
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