Dr Ali al-Saleh, imam at the Shia mosque in Milltown in Dublin, has warned that Islamic extremists are active in Ireland.
He said Ireland is not doing enough to combat the threat of ISIL, the terrorist group which controls vast swathes of Iraq and Syria.
"They (ISIL members) live here, they are active at the level of small circles, giving lectures, talking to the youth," Dr Saleh told Newstalk Breakfast.
"This is a problem. We've said that from the beginning, now we have it. We didn't tackle it from the beginning. It is a duty of us, the Imam, to talk openly against those things.
"I ask the Muslims here to cooperate with the gardai and to notify them about any activities like this," he added.
Dr Saleh's son Jaafar, a medical student, said he has heard a lot of people getting excited about what's going on in Iraq and Syria, with individuals speaking about their friends trying to join the fighting.
"You get a lot of speakers coming here from all over the world, from Saudi Arabia, from the Gulf states. (It's) sometimes kind of shocking that they're allowed into Ireland. Back over there where they speak, in Saudi Arabia or whatever, clearly they call for people to go to jihad in Syria and Iraq," he added.
Thanks to Dr al-Saleh, gardai prevented a controversial Muslim cleric, who "preaches hatred", from entering Ireland..
Mohammed al-Arifi, a Wahhabi preacher from Saudi Arabia, had been due to come here "for a few months", said Dr al-Saleh
Dr Saleh said, when Arifi decided to come to Ireland for a few months, "our people complained to the gardai and the gardai stopped him from coming".
He described the cleric as "a very well-known preacher, who preached hatred". Wahhabism is a fundamentalist religious movement of Sunni Islam.
He said prominent Muslims in Ireland "need to notify the gardai and the Government about the danger of allowing those visitors coming from outside".
It was his children who told him the cleric was on his way here Dr Saleh said.
"We objected to the gardai and the gardai thankfully listened to us and stopped him from coming," he said.
Earlier this year, Britain banned Arifi in an effort to deter young Muslims from going to join Islamic militants in Syria.
Arifi has called for jihad against President Bashar al-Assad of Syria.
"We can confirm Mohammed al-Arifi has been excluded from the United Kingdom," a statement from the British authorities said at the time.
"The government makes no apologies for refusing people access to the UK if we believe they represent a threat to our society.
"Coming here is a privilege that we refuse to extend to those who seek to subvert our shared values," it added.
Arifi tweeted a link to a statement, saying he rejected "allegations that he may have contributed to the radicalisation of three British-born Muslims".