As radical Islam spreads through the United Kingdom, US President Barack Obama has sent a special CIA unit to interrogate senior British security experts. The move is seen as a snub of Britain’s MI5 and MI6 intelligence agencies.

Up to 450 radical Islamic men from Great Britain have flocked to the battlefields in Syria and Iraq, joining the Islamic State of Iraq and Syria (ISIS), Lahoor Talabani, director of counter terrorism for the Kurdistan Regional Government (KRG), told Sky News in mid-June. A British Labour MP, Kahlid Mahmood, told the Sun that up to 1,500 UK militants are fighting in Syria. Talabani’s comments echoed those of British Prime Minister David Cameron, who said that 65 people have been arrested in the past 18 months for jihadist activities related to Syria. UK authorities have launched a campaign to encourage Muslim women to inform on relatives they suspect of planning to travel to the war-torn countries where ISIS holds large swaths of land.

Last week, the UK banned a radical group called Need4khilafah for incitement to terrorism, the Daily Mail reported. A leading hate preacher for the group, Abu Waleed, was linked to the “brainwashing” of three Welsh jihadists fighting in Iraq and Syria. Two of those young men, 20-year-olds Reyaad Khan and Nasser Muthana, have appeared in an ISIS recruitment video. Khan trained for holy war by practicing mixed martial arts at a gym in Cardiff, Wales.

British security forces have been “forced to admit they are struggling to keep track of the estimated 500 Britons who have travelled to the Middle East to fight alongside” ISIS, the Daily Mail reported on Sunday.

Since the US normally relies on information from MI5 and MI6 for intelligence within the UK, it is unusual for the CIA to send a team to investigate the country’s closest ally. Their primary goal is to establish the “stability” of the relationship between Sunni and Shia Muslims in Britain.

“The US is worried about the British situation. They fear there might be a knock-on effect for them,” Professor Anthony Glees, of the Centre for Security and Intelligence Studies at Buckingham University, said to the Daily Mail. “The throat-cutting between Sunnis and Shias in Iraq and Syria has not yet spread to the UK, but it is a real threat. It is conceivable you could see Shia ‘hit squads’ in Britain targeting Sunnis preparing to go out to the conflict zones to fight.”

“The Americans regard the UK as a disaster because of our lax stance on immigration which has allowed this militancy to take hold,” Glees added. “Frankly, they would not be doing their jobs properly if it did not do this – forming an objective view of the situation outside of the reports they get from MI5 and their officers at the US Embassy in London.”

As US concerns over radicalization of the UK’s Muslims and over foreign fighters returning to Europe from Syria and Iraq deepens, the US is discussing an increase in security measures at airports within America and abroad, ABC News reported. The Obama administration is focused on a new generation of bombs that terrorists in Syria could smuggle onto commercial flights.

“[This threat] is different and more disturbing than past aviation plots," one source told ABC News. Intelligence agencies, including the Department of Homeland Security and the FBI, have been debating their options for months, and top-level officials met at the White House last week to discuss the issue.

The battle-hardened foreign jihadists fighting in Syria and Iraq pose a threat to Western nations because they will be able to enter the countries without visas on European passports.

"We've seen Europeans who are sympathetic to their cause traveling into Syria and now may travel into Iraq, getting battle-hardened. Then they come back," Obama told NBC News in an interview broadcast Sunday.

According to the Daily Mail, the Obama administration has become “increasingly anxious” about “strong links” between American and British radicals, and the potential for American Muslims to follow the lead of their UK counterparts in fighting alongside ISIS. The CIA feels British efforts to provide a reliable assessment of the threat posed by and identify the members of radicalized Western Muslims have been inadequate, sources from the American spy agency told the Daily Mail.