Four properties in Brighton and Hove have been searched by officers from Sussex Police and the South East Counter Terrorist Unit.
Search warrants were issued by magistrates under the Terrorism Act 2000.
One of the properties searched was the family home in Arundel Road East, in Saltdean, of Abdullah Deghayes, who is believed to have been killed in fighting in Syria last month.
Abdullah, 18, is thought to have been killed alongside rebels fighting the regime of President Bashar al-Assad.
He is believed to have gone to Syria with his two brothers Amer, 20, and Jaffar, 16. Amer was reported to have been injured in battle by a shot to the stomach.
Abdullah went to Longhill High School and had been planning to go to Brighton University.
His father Abubaker Deghayes is reported to have said that his son went to Syria without his consent.
Abdullah’s uncle Libyan-born Omar Deghayes, 44, returned to Brighton in 2007 after being held without trial at Guantanamo Bay for five years.
Mr Deghayes, a victim of mistaken identity, was later paid compensation by the government over his detention as an enemy combatant.
Sussex Police said yesterday (Tuesday 20 May): “Material which may be relevant to the inquiry, which is looking into whether any offences against the act may have been committed, is being taken away for examination but no arrests are anticipated today.
“All police officers and staff involved in the searches are unarmed and local officers and PCSOs are helping to provide security outside the premises as well as local reassurance that this is not in response to any immediate threat to local communities.
“Local community groups are being briefed about the operation.”
Chief Superintendent Nev Kemp, the divisional commander in Brighton and Hove, said: “This is a necessary part of our continuing work to safeguard communities locally and nationally, including those who have links to Syria.
“Every step is being taken to ensure the operation is carried out sensitively, thoroughly and professionally.
“We understand what a distressing time this is for the family and we do not want to cause further distress to them.
“It is important, for strong operational reasons, that we carry out these searches as part of our ongoing inquiries into events in Syria.
“We are carrying out the searches as quickly and sensitively as possible.
“I can give local people an assurance that this is not in response to any immediate threat to local communities and anyone who does have any concerns can contact our local officers for further reassurance.”
Sussex Police said: “The Foreign and Commonwealth Office advice is that the whole of Syria is unsafe and people should not travel there.
“The best way to show support for those suffering in Syria is through registered charities and the Home Office have produced guidance to assist with this.”
