A total of four men have been arrested under anti-terrorism law following an operation in Clackmannanshire.
Forensic experts carried out an examination at the scene
Atif Siddique, 20, was detained in Alva on 13 April.
Mr Siddique's older brother, Asif Siddique, 24, and his uncle Mohammed Rafiq, 40, were detained at an address in Alva at about 0900 BST on Monday.
A third man, 46-year-old Mohammed Niaz, 46 from Bridge of Allan, near Stirling, was detained later in the afternoon, Central Scotland Police confirmed.
The arrest followed the search of a property in the town.
The men arrested are being held at Govan police station in Glasgow.
The family solicitor Aamer Anwar condemned the earlier two arrests on Monday and said the men should be released.
He said: "I strongly condemn police tactics which are a sign of increased desperation to widen the net.
"This is a respectable family, who since the arrest of their son, have fully co-operated with the police in their inquiries, yet find themselves being terrorised in this manner.
"The Siddique family are deeply distressed and anxious that both Asif and Mohammed Rafiq who have committed no crime are released immediately."
BBC Scotland reporter Duncan Kirkhope, who witnessed part of the Bridge of Allan operation, described seeing "a sea of police and vehicles".
Police conducted an operation in Bridge of Allan
He said he was driving through the main street in Bridge of Allan with his son just before 0930 BST on Monday when he saw police motorbikes blocking off the narrow one-way Union Street in the town centre.
"I looked down the street and all I could see was a sea of police and vehicles - mainly uniformed officers and marked police cars," he said.
"By the time we got parked and walked round a number of the marked vehicles drove away and then we saw people being driven away from the semi-detached house in unmarked police cars.
"One unmarked car had three Asian people in the back, possibly two women and a young person or a woman and two young people."
The other car - a Peugeot - had one Asian male, possibly in his 50s, in the back seat.
No-one appeared to be handcuffed.
"Then the forensic teams moved in from several vans. They took boxes into the two-storey house along with camera equipment," our reporter added.
"I saw eight or nine people in white suits going in the front door of the house or round the back. Another van stood outside with five or six more in it."
Police were granted more time to question Atif Siddique, with his detention period due to expire on Thursday morning.