UK police arrest 6 on terror charges amid heightened security fears Police officers stand next to passengers from a bus after it stopped and was surrounded by armed police on highway near Litchfield in central England on Thursday. Updated 8:30 a.m. ET: Armed British police carried out early-morning raids Thursday in London, arresting six people in what they called a pre-planned anti-terror operation. Just hours later, armed police evacuated around 50 people and closed a major toll road in both directions in Central England after a passenger on the bus was reportedly seen pouring liquid into a box, which then started smoking. Police later said the operation involving the bus was "not being treated as a terror-related incident." The operations came amid heightened security ahead of the London Olympics, which begin on July 27, though officials said the terror arrests were not linked to the upcoming games. Police didn't identify the suspects, who range in age from 18 to 30 and included five men and a woman. However, Mizanur Rahman, who is involved with a Muslim activist group, said all those arrested were British Muslims. He said the three men taken into custody in Stratford, the neighborhood that contains Olympic Park, were brothers and claimed that one was a former police officer. A police press officer declined to comment on the claim. Resident John Smallshaw said a raid took place at a residence on Abbey Road, only about a mile from the Olympic Park. He told The Associated Press he was awoken just after 4 a.m. by "five loud bangs in quick succession" and saw police raiding the home. He said he later witnessed "one young man taken on foot to a waiting ambulance." Another man was later taken into an unmarked police car, Smallshaw said, adding that plainclothes officers were still at the premises. Searches are being carried out at eight separate addresses in east, west and north London and at one business in east London, police said. Rahman identified one of the addresses as being in Old Street, near London's financial district. Report: Fake bomb exposes London Olympic security Police said all the suspects have been taken to a southeast London police station. Bus operation Live aerial video of the bus operation showed around 50 passengers sitting on the road surrounded by armed police. Police declared the area safe about four hours after the incident began, the BBC reported. "This is not being treated as a terror-related incident," a spokesman for Staffordshire Police said in a statement. Earlier, a commuter told the BBC he was four vehicles behind the bus when security officials stopped the traffic. "I've never seen so many ambulances turning up, also armed police, helicopter and dozens of police cars," the man, Nick Jones, said. We were told to stay in our cars, keep windows up and not put air conditioning on. Terror suspect's eye color? Flying cameras know Intelligence officials say there has been an expected increase in chatter among extremist groups ahead of the games, but there are still no specific or credible threats targeting the Olympics. The terror level is labeled substantial, a notch below severe. A substantial threat level indicates that an attack is a strong possibility Msnbc.com and The Associated Press contributed to this report.