Police are searching the family home of one of nine Britons who allegedly tried to cross illegally into Syria.
Officers are at the home of Labour councillor Shakil Ahmed, whose son Waheed is among a group of five adults and four children being held in Turkey.
The Rochdale councillor said he had thought his son was on holiday and was shocked by news of his arrest.
The Foreign Office said it was unable to confirm when the nine people would be deported back to the UK.
Waheed’s aunt, Zadia Bi, two of her sons and one of their wives, were the other adults detained, Mr Ahmed said.
The group from Rochdale, which also included children aged one, three, eight and 11, was seized in Hatay near the Syrian border on Wednesday.
In a statement, Mr Ahmed said he wanted his son to come home “as soon as possible so I can find out what’s going on”.
“My son is a good Muslim and his loyalties belong to Britain, so I don’t understand what he’s doing there,” he said.
“If I thought for a second that he was in danger of being radicalised, I would have reported him to the authorities.
“He’s studying a degree in politics and sociology at Manchester University and has a good future ahead of him.”
Speaking to the Daily Mail, he added: “All I know is that they were on holiday and then the next thing I am told is that they have been arrested.”
The councillor had earlier said in a statement he thought his son was in Birmingham on a work placement.
Greater Manchester Police and the North West Counter Terrorism force have launched an investigation to establish why the group apparently tried to enter Syria.
All nine are expected to be sent back to the UK “in due course”, police said.
Assistant Chief Constable Ian Wiggett said: “What is obviously concerning is why a family were seemingly attempting to take very young and vulnerable children into a war zone; such a volatile and dangerous environment is no place for them whatsoever.”
He said the primary concern was the “safety and welfare” of the children, and efforts were being made to ensure a “full safeguarding strategy” was in place upon their return.
Officers had uncovered “no evidence whatsoever” of any imminent threat to the UK that was linked to the group, police added.
Mohammed Shafiq, chief executive of the Ramadhan Foundation, said the news was “deeply worrying”.
“The idea you can take young children into a war zone is despicable and we condemn those adults who have done this,” he said.
Usman Nawaz, 25, who was part of the last Labour government’s Young Muslims Advisory Group, attended the same school as Waheed Ahmed.
He said he didn’t believe Mr Ahmed’s education in Rochdale had anything to do with the journey he had taken but it was a question the Muslim community needed to address.
“Though the numbers are small we are seeing a constant drip-feeding of British Muslims either getting into the Islamic State or trying to get in,” he told BBC Radio 4’s Today programme.
“There are young Muslims growing up in this country who don’t feel a sense of belonging to this country.
“For some it probably is an adventure but for others they think they are doing something noble so it’s the narrative that’s being presented to them.”