British police arrested seven alleged Islamist extremists overnight in what law enforcement officials in England are calling the most significant such arrests this year, authorities told ABC News.
Six men, aged 25 to 32, were taken into custody by unarmed officers in Birmingham, England, as "part of a large pre-planned, intelligence-led counter-terrorism operation," led by the West Midlands Police force, according to a police statement. All were detained on suspicion of the "commission, preparation or instigation of an act of terrorism in the U.K.," police said.
One woman, 22, was also arrested for allegedly failing to provide police with information related to terrorism.
Law enforcement sources told ABC News police conducted the operation after intelligence was developed by MI5, the British domestic intelligence agency.
Police did not say how far along the alleged plot was but Marcus Beale, West Midlands Assistant Chief Constable, said that while the police investigation is still in its "early stages," he believed "it as necessary to take action at this time in order to ensure public safety."
The suspects are being questioned in the West Midlands Police area as authorities search more than a dozen locations -- mostly domestic residences -- believed to be associated with the alleged plot, police said.
The U.K.'s terror threat level was downgraded from "severe" to "substantial" in July, meaning authorities believe there is still a "strong possibility" of a terrorist attack.
In December 2010, British police arrested 12 men who were allegedly in the final stages of a major bomb plot against targets in the U.K. At the time, authorities said those potential attacks may have been inspired by al Qaeda.
The West Midlands Police force is the second largest in the country to London's Scotland Yard and covers three major cities of Birmingham, Coventry and Wolverhampton, according to the force's website.
The force had previously come under fire in 2010 when it told Birmingham residents it was using a 200-strong CCTV camera network to monitor vehicle crime and anti-social behavior, when the West Midlands counter-terror unit was actually using the cameras in a secret operation target and observe Muslim suburbs, according to a report by the BBC. The cameras were dismantled in May of this year.