A sixth man has been arrested in London by police in relation to a potential threat to Pope Benedict XVI's visit.
His arrest, at 1345 BST, came after five men were seized at 0545 BST after counter-terrorism officers received intelligence of a potential threat.
All six, who were street cleaners, have been taken to a London police station.
The BBC's Danny Shaw said the arrests were carried out as a precaution. Police are searching a number of premises.
At least five of the men were not British nationals.
The cleaners worked for Veolia Environment Services, a major contract cleaning company that works for Westminster Council.
Armed officers arrested the first five men at the company's Chiltern Street depot, Paddington, as they were preparing to go on shift.
In a statement from Scotland Yard, the Metropolitan Police said that the men had been arrested in a Terrorism Act 2000 operation, launched by officers from the force's Counter-Terrorism Command.
All six men were arrested on suspicion of the commission, preparation or instigation of acts of terrorism.
They are 26, 27, 29, 36, 40 and 50 years old and most are understood to be Algerian. Police are continuing to search eight residential premises in north and east London and two business premises in central London.
Officers have not found any hazardous items.