From the Jammu and Kashmir Liberation Front (JKLF) to the pro-Pakistan Syed Ali Geelani, all separatist groups criticised the US for taking into custody a man who they said espoused their cause.
The Federal Bureau of Investigation (FBI) has charged Fai, who heads the Kashmir American Council, for pushing the Kashmiri issue in Washington with Pakistan funding for over a decade.
Geelani, chairman of the breakaway Hurriyat group, called the arrest "a conspiracy by India to weaken the freedom struggle in Kashmir".
Ideologically, Fai is said to be closer to Geelani's parent organisation, Jamaat-e-Islami.
Separatist leader Shabir Shah said he was surprised. "We always believed America respects the cause of Kashmir," he said.
JKLF leader Bashir Ahmad Bhat said Fai "was peacefully highlighting the cause of the Kashmiri people. We hope he will be released soon".
Fai, now an American citizen, was born in Wadwan village in Badgam district, 18 km from here.
The mass of Srinagar's residents had a different view of Fai's arrest. Many had not even heard of him.
Fruit seller Mehraj-ud-Din told IANS: "I have heard his name for the first time. He must be a big man."
Said businessman Bashir Ahmad: "He must have been somebody very influential. What he did must be known to him and US government. My life remains the same, whether Fai is in jail or on bail."
Even the educated class had heard little of Fai and his activities.
Pouring contempt on intellectuals who write books or organise seminars, college teacher Muzaffar Ahmad said: "Our lives are threatened by turmoil and uncertainty."
The Jammu and Kashmir Police said Fai had figured in their suspect list for a long time.
"We have enough material against him," Jammu and Kashmir director general of police Kuldeep Khoda told reporters.
Many from Jammu and Kashmir have attended conferences organised by Fai in the US.