Police are carrying out terrorism related raids at five addresses across Merseyside.
Officers from the North West Counter Terrorism Unit and Merseyside Police have arrested a 31-year-old man on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism. He remains in police custody.
Searches are being carried out at addresses on View Road in Rainhill, St Helens and Prescot Road and Holt Road in Kensington, Liverpool.
The searches are expected to last several hours and possibly days.
Anyone with concerns about suspicious activity should contact local officers or the confidential Anti-Terrorist Hotline on 0800 789321.
A self-styled neo Nazi has been jailed for 10 years after planning to attack mosques on Merseyside.
42 year old Ian Forman was arrested after chemicals and explosives were found at his home.
Security has been tightened at two mosques when evidence was discovered they could have been the target.
A Nazi-sympathiser who planned to blow up a number of mosques has been jailed.
Ian Forman, of Birkenhead, was convicted of Engaging in Conduct in Preparation of Terrorist Acts contrary to the Terrorism Act 2006 at Kingston Crown Court.
Det Supt Ian Hassall from Merseyside Police says Forman had an obsession with Nazi dictator Adolf Hitler.
"Thankfully, we will never know how far Forman was prepared to go in acting out his racist fantasies.
"However, we do know that Forman had carefully selected a number of targets to meet his own means. Had he carried them out, his attacks could have caused considerable damage to both property and people at several Mosques.
A Nazi-sympathiser who planned to blow up a number of mosques has been jailed for 10 years. Ian Forman plotted to attack mosques in Merseyside and had built a bomb at his home in Birkenhead.
Forman first came to the attention of police in April 2013 while he worked as a receptionist at Manisty, a glass recycling firm in Ellesmere Port.
Colleagues found that he had been researching chemicals and explosive substances on the internet during work hours - a clear breach of company policy.
A teacher from Manchester has appeared in court accused of planning to help others commit acts of terrorism linked to Syria.
Jamshed Javeed, 29, from Levenshulme, is charged with the intention of assisting others to commit acts of terrorism and engaging in conduct in preparation for giving effect to his intention.
He was one of four people arrested at a property in Cringle Road in raids on Tuesday.
He was remanded in custody at Westminster Magistrates' Court.
He will next appear at the Old Bailey on 4 April.
A man from Manchester will appear in court accused of terror offences linked to Syria.
Jamshed Javeed, 29, was charged with the intention of assisting others to commit acts of terrorism and engaging in conduct in preparation for giving effect to his intention, Greater Manchester Police said.
Javeed, of Cringle Road in Levenshulme, is due to appear at London's Westminster Magistrates' Court.
Officers investigating a number of people suspected of being involved in travelling to, or supporting fighting in, war zones made four arrests on Tuesday.
Two men and a woman who were arrested alongside him remain in police custody for questioning, police said.
A teacher suspected of travelling to war-torn Syria to help others in the fight against rebels has been charged with terrorism offences.
Jamshed Javeed, 29, of Cringle Road, Levenshulme, has been charged with intending to assist others to commit acts of terrorism.