Five people suspected of planning to join protests against the G20 summit in London on Thursday have been arrested after weapons were found during a raid on a house in southwest England, police said on Monday.

Detectives said the five Britons, three men aged 16, 19 and 25 and two women both aged 20, were arrested in the city of Plymouth, between Friday and Sunday and were being held under counter-terrorism powers.

Police said their inquiries indicated there was no religious agenda to the investigation.

Thousands of officers are taking part in a massive security operation this week when world leaders arrive for the G20 summit on the financial crisis to be held on April 2.

Anarchists have threatened to bring chaos to the streets of the British capital and a police source told Reuters the five suspects were believed to be planning to take part in the protests.

Police sought to reassure local people, saying they were not at risk. These arrests would appear to be isolated at this time, said assistant chief constable Sharon Taylor of Devon and Cornwall police.

Those arrested people will remain in custody while further enquiries take place.

The first person arrested was a 25-year-old man, detained in Plymouth on Friday on suspicion of criminal damage.

A search of his home led to the arrest of three others for drugs offences, but detectives later found unspecified weapons and suspected imitations, and material relating to political ideology. The fifth man was arrested on Sunday and all five were then detained under the Terrorism Act.

(Reporting by Michael Holden; editing by Kate Kelland)