The mosque, set in a leafy suburb of south Manchester, has operated since being bought in 1967 by donors from the Syrian community.
Elders at the Didsbury mosque, a Victorian former Methodist chapel, also voiced concern about reports of Islamophobic attacks since the bombing at a pop concert which killed 22 people.
"The horrific atrocity that occurred in Manchester on Monday night shocked us all. This act of cowardice has no place in our religion," said Fawzi Haffar, a trustee at the mosque, joined outside the building by members of the Muslim community.
After a minute's silence, he thanked those who had helped victims and urged people to contact police with any information about the attack.
The mosque is set in a leafy suburb of south Manchester popular with university students. It has operated since being bought in 1967 by donors from the Syrian community.
"It's one of the most popular mosques in Manchester because they preach nothing but love here," Javed Akhtar, a regular attendee, told AFP as police stood guard outside the red-brick building.
Akhtar said he had not come across Salman Abedi, the 22-year-old attacker, whose family emigrated to Manchester from Libya.
But he said: "It's unbelievable that you get a guy from here, who's been here, who's done such a terrible thing."
The attack has prompted soul-searching in Britain's Muslim communities about homegrown radicals, as well as concerns about a possible backlash.
A woman arriving at the Didsbury mosque on Wednesday asked a police officer: "Are we all under arrest? We're all under suspicion, aren't we?"
Abedi's father had sometimes performed the call to prayer at the mosque and his brother Ismael had been a volunteer, according to media reports.
Haffar did not detail the attacker's relationship to the mosque, saying only that he had not been employed there.
"Some media reports have reported that the bomber worked at Manchester Islamic Centre (Didsbury mosque) in the past. This is not true," he told journalists.
One senior figure from the mosque, Mohammed Saeed, told The Guardian that when he once gave a sermon denouncing terror, Abedi stared him down.
"Salman showed me a face of hate after that sermon," Mohammed Saeed said of the 2015 encounter. "He was showing me hatred."
Since the attack, questions have mounted over how Abedi, born in Britain to a devoutly Muslim Libyan family, was radicalised and came to carry out a bombing claimed by the Islamic State group.
Azher Mahmood, a 57-year-old worshipper at the Didsbury mosque, said preachers there spoke out against radicalisation.
"They'll say stay away from ISIS (Islamic State), stay away from all these radical groups. They will preach that, tell the youngsters that," he told AFP.
"How he got radicalised I don't know. Whoever's done it I'm sure is not from this mosque."
Mahood suggested Abedi's path to extremism could have taken place online: "That's probably the worst place (for finding extremist content), I would say."
Mohammed Shafiq, from the Manchester-based Ramadhan Foundation, also pointed the finger at the internet and social media channels for radicalising young Muslims.
"I think you have to recognise and accept that the issue isn't mosques. A tremendous amount of work has gone into dealing with radicalising within mosques," he told AFP.
Extremists from the Islamic State group are distorting Islamic scriptures online to radicalise people, Shafiq said.
But he admitted more needed to be done to create dialogue with young people, whose voices have been "consistently dismissed" in everyday life.
In Didsbury, there were fears the bombing would lead to reprisals against the Muslim community.
Hours after the arena attack a man set fire to the entrance of a mosque in the Oldham area of the city, according to a video published by the Manchester Evening News.
"We are concerned about reports we are receiving about anti-Muslim acts, ranging from verbal abuse to acts of criminal damage to mosques," said Haffar.
But despite such concerns, he said the mosque remains proud to be part of the community: "Manchester is a great city with a great history and a prosperous and bright future ahead of it."