A major security breach in British government communications has been uncovered by GCHQ, a report says. Hackers allegedly associated with Islamic State collected information on key UK cabinet ministers.

UK Government Communications Headquarters (GCHQ) has exposed ISIS-linked extremists intercepting classified emails of PM David Cameron’s cabinet, The Telegraph reports. One of the senior ministers implicated in the scandal is Home Secretary Theresa May.

By gaining access to government emails, ISIS-linked malefactors could learn which events top British officials and members of the royal family were preparing to attend.

According to PM Cameron, Islamic State was planning “barbaric attacks against the West,” with terror plots targeting “high-profile public commemorations” last summer.

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In late August, it was reported that a 21-year-old UK-born hacker, Junaid Hussain, believed to be the leader of Islamic State’s cyber division, was killed in a US drone strike near the Syrian city of Raqqa, the power base of Islamic State (formerly ISIS/ISIL).

Hussain allegedly led Islamic State’s hacker group dubbed CyberCaliphate. In 2012, he was sentenced to six months in prison for stealing former British Prime Minister Tony Blair’s address book from an online account. After serving a prison term, he moved to Syria and joined the jihadists.

Cameron has said that Hussain and British ISIS fighter Reyaad Khan were killed in an RAF drone strike on August 21 in Syria.

Killer drones hunting British jihadists for months, govt admits http://t.co/QVZV4sKXh5pic.twitter.com/biaJFwxloS — RT UK (@RTUKnews) September 9, 2015

Reportedly, the cyber threat became evident in May, when GCHQ exposed plans to attack Britain.

Earlier this month, it was revealed that the British government has drawn up a “kill list” of foreign-based jihadists shortly after the UK general election in May.

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Defence Secretary Michael Fallon said last Monday that the government would not hesitate to carry out further attacks against IS targets.

“They have plans to mount a series of attacks on Britain and our job is to identify those attacks, the terrorists and where we can forestall them,” Fallon told ITV’s Good Morning Britain.

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What information exactly have been stolen remains unclear, while The Telegraph reports that “no security breaches occurred” and the officials were simply recommended to tighten cyber security measures, which eventually took the form of changing passwords.