(BBC) A fourth Iranian man has been arrested as part of a counter-terrorism investigation in London.
The Metropolitan Police said the 31-year-old was detained in north-west London on Friday morning under the National Security Act.
Three other men — all from Iran and aged 39, 44 and 55 — were arrested in London on 3 May as part of the investigation.
Police have obtained warrants to hold those three men until 17 May.
Police said searches were carried out at two addresses in north-west London on Friday.
