LONDON — British counter-terrorism police charged at least one suspect on Saturday in connection with a security incident at RAF Lakenheath, a United States-operated air base in Suffolk, the Metropolitan Police said.

The investigation began earlier in the week when a dual UK-Iranian national was detained over a breach at the base, which hosts American military aircraft. Counter Terrorism Policing confirmed that six people, including a British-Iranian man, had been arrested as part of the probe.

The Crown Prosecution Service authorised charges under the Terrorism Act. Officers continued to search several properties in eastern England, and some of those arrested remained in custody pending further questioning, police said.

Prime Minister Andy Burnham, who said earlier in the week that there were "serious questions" to answer about base security, is expected to face pressure in Parliament over the breach. The US Air Force confirmed it was cooperating fully with British authorities investigating the incident.

RAF Lakenheath houses the 48th Fighter Wing and has been central to American air operations in Europe. Security around US installations in Britain has been heightened following regional tensions involving Iran, according to the Ministry of Defence.