LONDON - British police were questioning four men Monday on suspicion of terrorism after a string of arrests that included armed officers shooting out the tyres of a car near the Tower of London.Reports in British media said the men had been arrested in coordinated raids across London on Sunday night that were aimed at preventing an alleged terror plot involving the use of guns.Police said they were still searching six premises and two vehicles on Monday.Armed officers arrested two 25-year-old men -- one a British national of Turkish origin and the other a Briton of Algerian origin -- in a street in east London. A 28-year-old British national of Azerbaijani origin was arrested at a house in Notting Hill, west London, and a 29-year-old Briton of Pakistani origin was arrested in a street in Peckham, southeast London.A Metropolitan Police spokesman said so-called Hatton rounds -- special shotgun ammunition used to breach doors and tyres -- were "specifically used to disable a car" in the arrests in east London."They were used to shoot at tyres. No one was injured," the spokesman told AFP.The arrest took place in a street about 200 metres from the Tower of London, one of London's busiest tourist attractions.Armed officers were involved in all of the arrests.All four men were being held at a police station in south London on suspicion of the commission, preparation or instigation of acts of terrorism.Under British counter-terror laws the suspects can be held for 48 hours and police can then apply for warrants to hold them for up to 14 days from the time of arrest.Police said the raids were the result of a "pre-planned intelligence operation" and added that "public safety remains our overriding concern".The BBC quoted government officials as saying that a decision to act was taken on Sunday to dismantle the "potentially very serious" plot, although it was not on the scale of previous large-scale bomb plots.A witness to the arrest in Notting Hill, in an upmarket street lined with boutiques and restaurants, said the arrested man "didn't look like a terrorist".Ramin Massodi, a worker at a Persian restaurant, said specialist officers in several cars pushed the suspect up against the glass of the restaurant."I heard shouting then I looked outside and saw four cars... and they grabbed him," he said.London has experienced a number of terror attacks in recent years, including the July 7, 2005 bombings on the transport system in which four Islamist suicide bombers killed 52 innocent people.