An Islamic cleric in Dublin has urged Muslims to do all they can to identify extremists.
Shaykh Dr Muhammad Umar al-Qadri, who has defied threats from fanatics to condemn the attacks in Manchester, London, Paris and Brussels, warned that EU countries should now consider deporting the hate-mongers.
He admitted the latest atrocity had left him stunned. "My heart goes out to all affected," he said.
He said it was up to each Muslim to support the fight against terror.
"Isil plans its attacks to create more division and hatred in our societies," he said. "As Muslims, we must seize the Islamic costumes from these terrorists. May God grant us all the ability to stand united with love and compassion in the face of this terror and eradicate this fanaticism."
Mosques in Dublin, Cork and Belfast have also expressed their solidarity with the victims of the Manchester attack.
"We must clean our own back yard by identifying individuals that support the Isil mentality," Dr al-Qadri added. "The greatest threat to Islam and humanity comes from Isil and other such extremist so-called jihadis. Let us unite to get rid of the extremism."
He also warned he would not be intimidated by hate messages posted on social media.
"Call me a traitor or whatever you want, but I will not stop speaking out," he said. "As Muslims it is our religious obligation to speak out against extremists."
Dr al-Qadri, who helped to establish a website initiative to help prevent radicalisation, said Europe had to get tough with those who promote hate.
"I strongly support legislation that bans hate preachers from entering the EU and also deports their sympathisers," he said.