Counter-terrorism police and MI5 officers say they have broken up a suspected Christmas bomb plot after arresting four men in a series of early-morning raids who continue to be questioned.

Armed police blew open doors while raiding addresses in South Yorkshire and Derbyshire on Tuesday after intelligence suggested the men were planning to build or acquire a bomb in an Islamist plot to strike a target in the UK.

The suspects are understood to have been under surveillance, but counter-terrorism officers decided to act amid concerns that they had moved beyond discussion and begun trying to source bomb parts or materials.

Bomb squad officers accompanied armed police as a precaution to at least one of the addresses and witnesses heard loud bangs as police blew doors open to gain entry.

Counter-terrorism sources described the arrests as "significant". They come at a time when police have stepped up security at possible seasonal targets including Christmas markets.