Income from oil has helped boost terror group's cash reserves to $1billion and enables ISIS to pay fighters an estimated wage of $1,000 every month

ISIS generates up to $2million a day from its vast oil production industry

Saudi and UAE air forces conducted majority of strikes, with U.S. support

Terrorists fighting for ISIS in Syria are believed to have freed 150 prisoners in the group's de facto capital Raqqa in the hope it will convince America and its Arab allies to end a campaign of airstrikes.

American jets hit scores of key oil refineries last night, and the Pentagon displayed photos of the facilities in ruins today.

The strikes prompted desperate militants to released scores of captives overnight, apparently in the belief the move could encourage an anti-ISIS coalition of nations to focus their raids away from Raqqa.

The militant stronghold is widely thought to be a base for the group's senior figures - including leader Abu Bakr al-Baghdadi - and where British hostages Alan Henning and John Cantlie are being held.

The 150 prisoners released by the group are all believed to have been arrested in recent weeks, suggesting they are most likely to have been locals accused of committing minor crimes.

The news comes as a fresh wave of airstrikes from the United States and its Arab allies hit ISIS oil refineries overnight, killing at least 14 militants and striking at the heart of the terror group's funding.

ISIS generates up to $2million a day from the sale of oil, employing highly trained engineers to extract thousands of barrels a day from the vast swaths of Syria and Iraq under the terror group's control.

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Flattened: Before and after aerial pictures show damage to the Gbiebe Modular Oil Refinery in Syria following air strikes by U.S

Hitting where it hurts: The ruins of the Jeribe Modular Oil Refinery in Syria. At least 14 militants were killed in the latest strikes

Daylight flight: Activists based in Syria's de facto capital Raqqa claim to have spotted aircraft belonging to the anti-ISIS coalition carrying out raids in the area this morning

Airstrikes: A jet lands on USS George H. W. Bush Tuesday after successful strikes against ISIS targets in Syria

Force: A handout picture made available by the US Department of Defense today shows a formation of US Navy F-18E Super Hornets refueling having carried out airstrikes on targets linked to ISIS

The Saudi and UAE air forces conducted a majority of the coordinated attacks last night, targeting 12 'modular oil refineries' in eastern Syria capable of extracting thousands of barrels of crude oil a day.

Much of this oil is believed smuggled into neighboring oil-producing regions at reduced price and then sold of mainstream markets, with the entire process helping ISIS become the wealthiest terror group of all time, with an estimated $1billion in cash reserves.

The U.S. provided strike capability as well as surveillance aircraft to the overnight strikes in Syria, Pentagon spokesperson Navy Rear Admiral John Kirby

Last night's 13 airstrikes were aimed at 12 sites, 'using a mix of fighters, bombers and Tomahawk missiles', he added.

At least 14 militants are believed to have been killed - along with a further five people who lived near one of the refineries in northeastern Hassakeh province.

It is believed the civilian victims are most likely wives and children of the militants.

Prepared: A US Air Force pilot is seen moments before taking off in support of a mission to strike ISIS

Plans: In this image released by the U.S Department of Defense today, Air Force Master Sgt. Jeffery Morris goes through paperwork before taking his fighter jet to conduct air strikes in Syria

Defiant: A fluttering ISIS flag is flown over a hill in Tel Abyad, on the Syrian-Turkish border yesterday. The area, which is in the heart of the Raqqa countryside, has been the subject of numerous coalition airstrikes

RADICAL PREACHER ANJEM CHOUDARY IS ONE OF NINE MEN ARRESTED BY COUNTER-TERROR POLICE IN LONDON ON SUSPICION OF ENCOURAGING TERRORISM Radical preacher Anjem Choudary is understood to be one of nine men arrested today as part of an investigation into Islamist terrorism. Choudary, 47, and eight other men aged 22, 31, 31, 32, 36, 38, 39 and 51 were arrested by Metropolitan Police officers in London this morning, and have all been taken to police stations - where they remain in custody. Some 19 residential, business or community premises were also being searched today as part of the investigation, Scotland Yard said. Eleven of these were in east London, one was in west London, one was in north-west London and five were in south London - while a residential address was also being searched in Stoke on Trent, Staffordshire. A police spokesman said: ‘These arrests and searches are part of an ongoing investigation into Islamist-related terrorism and are not in response to any immediate public safety risk.’ Officers confirmed that the nine men were arrested on suspicion of being a member of a proscribed organisation, supporting a proscribed organisation and encouraging terrorism. Al-Muhajiroun is understood to be the banned organisation in question, sources said this morning. Advertisement

According to Foreign Policy, the 'modular' operations targetted in the attacks refine crude oil that is later smuggled and sold in Turkey and Iraqi Kurdistan.

A U.S. official speaking on condition of anonymity said the strikes were aimed at infrastructure and support structures around the oil platforms - including barracks.

Most of the strikes had been successful, he explained, adding that although some of the refinery towers are remain standing the systems needed to operate machinery have been destroyed.

U.S. Central Command said the refineries and the highly-skilled engineers who operate them have been producing between 300 and 500 barrels of refined petroleum daily, after militants seized control of the majority of Syria's oil fields earlier this year.

According to King Abdullah of Jordan, the vast sums of money generated from the sale of oil has helped ISIS pay fighters $1,000 per month - an upper middle class income in his country.

The latest strikes came on the third day of a U.S.-led air campaign aimed at rolling back ISIS in Syria, and was aimed at one of the militant group's main revenue streams.

The U.S. has been conducting air raids against the group in neighboring Iraq for more than a month.

At least four oil installations and three oil fields were hit around the town of Mayadeen in the eastern province of Deir el-Zour, according to the Britain-based Syrian Observatory for Human Rights and two local activist groups. A third activist group loyal to the militants confirmed the reports.

At least 14 militants were killed, said the Observatory, which gathers information from a network of activists on the ground.

Another five people who lived near one of the refineries in the northeastern Hassakeh province were also killed, the Observatory said, adding that they were likely the wives and children of the militants.

Strong presence: Military leaders have said about two-thirds of the estimated 31,000 Islamic State militants were in Syria. The U.S. has also been increasing its surveillance flights over Syria, getting better intelligent on potential targets and militant movements

Death: Members of Iraqi SWAT troopers and an Iraqi Shiite cleric (top left) inspect the dead bodies of ISIS militants during an intensive security deployment north of Muqdadiyah in Diyala province yesterday

Residents buy bread from a bakery in Tel Abyad on the Syrian-Turkish border yesterday. The area, which is in the heart of the Raqqa countryside, has been the subject of numerous coalition airstrikes

Business as usual: Herders watch their sheep in Tel Abyad - a ISIS stronghold on the Syrian/Turkey border

Last night's strikes marked the third wave of an anti-ISIS air offensive led by the U.S. with broader support from five Arab nations: Bahrain, Saudi Arabia, Jordan and United Arab Emirates.

Although ISIS' finance centre in its de facto capital Raqqa was hit in the first wave of air strikes, last night's raid is believed to be first time ISIS' production and sale of oil has been directly targetted.

'We are still assessing the outcome of the attack on the refineries, but have initial indications that the strikes were successful,' the Pentagon said in a statement.

'These small-scale refineries provided fuel to run ISIL operations, money to finance their continued attacks throughout Iraq and Syria, and an economic asset to support their future operations.'

On Monday, Bahrain, Saudi Arabia, Jordan and United Arab Emirates joined the U.S. in airstrikes against Islamic State targets in Syria, with Qatar playing a support role.

On Tuesday, Central Command said the U.S. had conducted airstrikes that hit at least 20 locations in Syria. Combat aircraft flew 64 sorties.