LONDON (Reuters) - British police were questioning two men Sunday after a parcel bomb was sent to the headquarters of the MI6 foreign intelligence service and another was intercepted at a postal sorting office.

"The Metropolitan Police Service is investigating two suspect packages addressed to premises in central London," a Scotland Yard spokesman said, declining to give details of the devices.

He said the parcels were found Wednesday and Thursday. Two suspects, aged 52 and 21, were arrested in North Wales the next day and brought to London, where a magistrate granted warrants Saturday for further detention and questioning.

Located on the bank of the River Thames, the fortress-like headquarters of MI6 -- more formally known as the Secret Intelligence Agency -- suffered superficial damage in a rocket attack by dissident Irish republicans in 2000.

(Reporting by Mark Trevelyan, editing by Jonathan Thatcher)