British police have arrested a fifth suspect in an alleged terrorist plot.
He joins four other men in their early 20s arrested after raids across London Tuesday.
Officials have given no details on the planned attack, but said it was in the early stages and described it as significant and serious. At least one of the suspects is alleged to have ties to Islamic militants in Syria.
Britain raised its terrorist threat level to severe in August.
The Islamic State in Syria has beheaded two British aid workers and two U.S. journalists to avenge U.S.-led airstrikes on the Islamic State in Iraq.