"The arrests were intelligence-led and pre-planned as part of an ongoing investigation by Counter Terrorism Policing North East and (domestic security agency) MI5," West Yorkshire Police said in a statement on Tuesday.
"The public may have heard loud bangs at the time police entered the properties. We would like to reassure them that this was part of the method of entry to gain access,” the statement added.
Three men, aged 22, 36 and 41, were held after raids at their homes in Sheffield and a 31-year-old was detained nearby Chesterfield early Tuesday.
The police gave no details about what the men were suspected of planning. They are being questioned on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism.
Terrorist attacks so far this year have killed 36 people and hurt 200 in Westminster, Manchester, London Bridge and Finsbury Park. They were all carried out by people radicalized within the UK.
On December 6, two men were held in police custody in Britain after authorities foiled their plan to assassinate Prime Minister Theresa May, according to the country's counter-terrorism security service.
May has been on many occasions criticized over her disproportionate attention to what she calls the threat from “Islamic extremism” while failing to notice the rise in the far-right terrorism threat.
UK Home Office figures have shown that nearly one third of people being monitored under the Channel anti-terror program in 2016-17 leaned towards extreme right-wing ideologies and were vulnerable to radicalization.