Rochdale councillor Shakil Ahmed said he had thought his son Waheed, 22, was on a work placement in Birmingham.
The group - which also included children - from Rochdale were seized near the Syrian border.
In a statement, Mr Ahmed said he wanted his son to come home "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."
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.
Gail Hopper, director of children's services at Rochdale Borough Council, said the authority was "aware of the situation" and co-operating with police.
The group was detained by Turkish authorities at Reyhanli, in Hatay province, near the Syrian border on Wednesday.
They were taken to a police station in southern Turkey overnight, and then sent to a department for foreigners awaiting deportation to the UK.
The UK Foreign Office has said it is in contact with the Turkish authorities.
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 progamme.
"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."
The revelations about the group from Rochdale follows a string of cases where British citizens have tried to reach Syria.
Last month three young men from north-west London were arrested in Turkey, following a tip-off from British police, and were flown back to the UK.
In another case, three schoolgirls from east London are believed to have followed a fourth girl to the region. All four teenagers are thought to have reached Raqqa, the Syrian city where Islamic State (IS) has its headquarters.
About 600 Britons are believed to have gone to Syria or Iraq since IS militants seized control of large swathes of territory there.
And the United Nations estimates the number of foreign fighters joining militant groups in the region is more than 25,000 - from 100 different nations.
One of nine Britons detained in Turkey for allegedly trying to cross illegally into Syria has been named as the son of a Labour councillor.