Government forces are battling to push back ISIS (Islamic State in Iraq and the Levant) and its Sunni Muslim allies in Diyala and Salahuddin provinces, after the militants overran the second city, Mosul, last week.

In other developments:

UK Prime Minister David Cameron told Parliament in London that ISIS was also plotting terror attacks on Britain
India confirmed that 40 of its citizens had been kidnapped in the violence-hit Iraqi city of Mosul
Saudi Foreign Minister Saud bin Faisal warned that Iraq faced the risk of civil war
Turkey is investigating reports that 15 Turkish builders were abducted by ISIS on Tuesday; 80 Turks were kidnapped in Mosul last week.

Militants 'in control'

The attack on the refinery started at 04:00 (01:00 GMT) from outside two of the three main entrances to the refinery, according to Reuters.

A view of the refinery in 2009

A watchtower at the refinery (archive image)

Alleged ISIS militants in the town of Baiji (taken from a video posted on 17 June)

Alleged ISIS militants in the town of Baiji in recent days

Smoke rose from a spare-parts warehouse and some stores of oil were reportedly destroyed.

"The militants have managed to break into the refinery," the unnamed official told Reuters from inside the refinery. "Now they are in control of the production units, administration building and four watchtowers. This is 75% of the refinery."

Army spokesman Qasim Ata said in news conference broadcast live on TV: "The security forces thwarted an attempt by ISIS to attack the Baiji refinery and 40 terrorists were killed."

Stories from inside Iraq refugee camp

The nearby town of Baiji was overrun by ISIS-led militants last week. Foreign personnel, including a small number of British nationals, were evacuated from the refinery earlier but local staff reportedly remained in place.

Baiji accounts for a little more than a quarter of the country's entire refining capacity, all of which goes toward domestic consumption for things like petrol, cooking oil and fuel for power stations, an official told AP news agency.

Hundreds of people have been killed since the start of the militant offensive last week, many of them believed to be captured soldiers publicly shot by ISIS-led firing squads.

During fighting in the city of Baquba this week, 44 prisoners were killed inside a police station in unclear circumstances.

'A setback'

Government forces have renewed air strikes on militants while militants in the western province of Anbar say they have made advances, with a number of police stations near the town of Hit going over to dissident tribes.

Further north, the Iraqi government said it had recaptured the citadel in the strategic town of Tal Afar, where militants were said to have taken control on Monday.

An army spokesman told the AFP news agency troops were planning to press on to militant-held areas in Mosul on Thursday.

Iraqi PM Nouri al-Maliki: "We will deal with those who think that they can defeat the political process"

"I would like to say once again that what has happened in Iraq is a setback but not every setback is a defeat," Mr Maliki said on Wednesday.

"This setback has allowed Iraq to recover its national unity and Iraqis have managed to recover their feeling that they are in danger and that not a single Iraqi will benefit from this crisis."

Mr Maliki has long been accused of favouring the country's Shia Muslim majority and fomenting unrest among the Sunni minority.

Iranian President Hassan Rouhani has said Tehran will not "spare any effort" to defend Shia holy shrines in Iraq against "mercenaries, murderers and terrorists".

He was speaking amid reports that the head of the elite Quds Force of the Iranian Revolutionary Guards, Qasem Soleimani, was in Baghdad to help co-ordinate the fight against the militants.

A Kurdish fighter monitors a road in Diyala province, Iraq, 14 June

Kurdish fighters are resisting the militants in the north

Iraqi women pass a car destroyed in a bombing in Baghdad, 18 June

Baghdad has been hit by new car bomb attacks since the Sunni offensive started

Iraqis at a food distribution at Khazir refugee camp outside of Irbil, 217 miles (350km) north of Baghdad

The government has insisted that food supplies are not in danger and that ISIS will not be

able to take Baghdad

Young Iraqis board a lorry at a recruiting centre in Baghdad, 14 June

Young Iraqis have been volunteering to serve in the battle with the militants

Volunteers train at military base in the Shia holy city of Najaf, 100 miles (160km) south of Baghdad, 17 June 2014

Correspondents have warned that Iraq could be on the brink of outright sectarian war between

Sunnis and Shias (seen marching here)

ISIS in Iraq

ISIS supporters demonstrate in front of the provincial government headquarters in Mosul, 360km (225 miles) north-west of Baghdad

The rebels now control the northern cities of Mosul and Tikrit

ISIS grew out of an al-Qaeda-linked organisation in Iraq

Estimated 10,000 fighters in Iraq and Syria
Joined in its offensives by other Sunni militant groups, including Saddam-era officers and soldiers, and disaffected Sunni tribal fighters
Exploits standoff between Iraqi government and the minority Sunni Arab community, which complains that Shia Prime Minister Nouri Maliki is monopolising power
ISIS led by Abu Bakr al-Baghdadi, an obscure figure regarded as a battlefield commander and tactician