The arrests come after the UK government said it would proscribe Palestine Action under anti-terror laws.
UK police have arrested four people in connection with a pro-Palestinian protest last week, in which military planes were vandalised at an airbase in England in an action claimed by the Palestine Action group.
Two activists from Palestine Action broke into the Royal Air Force base in Brize Norton, Oxfordshire, on June 20, damaging and spraying red paint over two planes used for refuelling and transport.
A woman, 29, and two men aged 36 and 24, were arrested on Friday on suspicion of the commission, preparation or instigation of acts of “terrorism”, while another woman, 41, was arrested on suspicion of assisting an offender, according to a statement by Counter Terrorism Policing South East (CTPSE).
The four arrests were made in London and Berkshire, in southeastern England, it said.
