Fianna Fáil leader Micheál Martin has said more clarity is needed on whether the Justice Minister had a role in Fine Gael by-election candidate Verona Murphy's visit to a centre for asylum seekers.
During an interview with Newstalk Breakfast, Deputy Martin addressed the controversy around the Wexford candidate's comments on asylum seekers.
He suggested they were "extraordinary comments".
Deputy Martin added: "To conflate ISIS with migration was a shocking thing to do, because they're not related.
"I do think the fact that the comments were withdrawn and denounced is important actually, and that people moved to clearly reveal the nonsense and the dangerous nature of those comments... in the middle of an election campaign."
He added: "I don't think Fine Gael knew about it... but I'm just not clear whether there was an attempt made to play to a certain sentiment in the election.
"I don't understand fully the sequence of events that led to these comments from Verona Murphy.
"Certainly Verona Murphy was quite comfortable making those comments at one stage of the campaign, and then when the pressure came on withdrew the comments and said she misunderstood the whole migration question."
He said questions over whether a decision was made locally to play on the issue "is open to consideration... I don't think we can discount that".
There has been criticism of a visit by Ms Murphy to visit a centre in Waterford to "gain a better understanding of asylum and refugee issues".
Deputy Martin suggested that the people in the centre were 'used' by Fine Gael, although added he "didn't know the full details" around the visit - including any role played by Justice Minister Charlie Flanagan.
He argued: "I think we do need more clarity around that - [including] the role of the Minister for Justice, who is the director of elections as well, and whether he used his influence."
Elsewhere, Deputy Martin cautioned against politicians using migration as an electoral issue.
He observed: "I've always felt there was a very strong consensus among political leaders across the political divide that we would never use migration as a vehicle for electoral or political leverage - we need to double down and recommit to that."
Deputy Martin said he was also 'surprised' by some recent comments from Leo Varadkar.
The Fianna Fáil leader explained: "The Taoiseach came out, for example, and just named Albanians and Georgians as problematic. Now why did he to do that in the middle of a debate around direct provision in Achill? I thought that was a mistake.
"I think Fine Gael are speaking out of both sides of their mouth on this, because they're nervous of it and they're not taking a clear line in it."
He added: "To be fair, I'm not saying they're in the same league as Deputy Noel Grealish was last week when he clearly premeditatedly went into the Dáil at a leader's questions, and I think made some very loaded points in terms of transfers of wealth back to other countries.
"He instanced Nigeria in particular, which turned out not to be factually correct."