The operation is understood to relate to a possible plot involving Islamist extremists with potential targets in the UK.
The threat was not thought to be imminent.
Some of those arrested are understood to be British nationals.
More top news
Anthony Birdee from Deptford in south east London tied the English bull terrier, named Muller, to a post in his garden.
A report warned overcrowded streets could lead to a 'Hillsborough scale' tragedy.
Southern got just one star for punctuality, reliability, seat availability, frequency and value for money.