Ukip MEP David Coburn is facing calls to resign after allegedly comparing SNP minister Humza Yousaf to convicted terrorist Abu Hamza.
Yousaf, the Scottish Government's Minister for Europe and International Development, said he was "appalled, disgusted and hurt" by the "Islamophobic" comment reported in the Scottish Daily Mail.
The MSP for Glasgow has written to Ukip leader Nigel Farage calling for Mr Coburn to be suspended while an investigation takes place.
First Minister Nicola Sturgeon condemned the alleged remark as "reprehensible" while Scottish Conservative leader Ruth Davidson described it as "totally unacceptable" and Scottish Labour's deputy leader Kezia Dugdale said it was a "disgusting slur".
Scots Liberal Democrat leader Willie Rennie said the reported comment was "astonishing" and labelled Mr Coburn "an offensive fool".
But Ukip's Scottish chairman, Arthur Misty Thackeray, denied the comparison had been made, saying his party colleague made a "slip of the tongue" and "got a name wrong".
Coburn, Ukip's only elected member in Scotland, is said to have made the remark during a conversation with the paper regarding his appearance on the BBC's Big Immigration Debate on Tuesday.
He is reported to have claimed that Yousaf was supposed to appear on the show, before stating: "Humza Yousaf, or as I call him, Abu Hamza, didn't seem to turn up."
David Coburn's 'Abu Hamza' slur against @HumzaYousaf is derogatory and utterly appalling. He should resign immediately.— Ewan McQueen (@ewanmcqueen_91) March 14, 2015
David Coburn on @HumzaYousaf: 'As I call him, Abu Hamza' - Man alive how offensive can this guy get?— Ross McCafferty (@RossMcCaff) March 14, 2015
The MEP, who is standing for Ukip in the Falkirk constituency at the general election, is said to have told the paper that the remark was intended to be private.
Yousaf said: "I am utterly appalled, disgusted and hurt by the comments allegedly made by David Coburn MEP. This is Islamophobia of the worst kind.
"If this was shouted at a Muslim on the street none of us would tolerate it. The fact this abuse has come from an elected member of the European Parliament is even more shocking and completely unacceptable.
"Nigel Farage has been plagued by accusations of leading a racist party and this outburst from David Coburn MEP shows that Ukip are not just a party with a few rotten apples but rotten to the core.
"If Nigel Farage is serious about Ukip being a party that will not tolerate xenophobia in any form then I expect David Coburn to be expelled from Ukip immediately and have written to Nigel Farage in that vein."
Yousaf added: "David Coburn has been exposed making Islamophobic remarks and should do the honourable thing and resign."
His letter to Farage reads: "I am sure you will wish to distance Ukip from such attitudes and I note you have taken disciplinary action against those found to make such prejudiced remarks in the past.
"I therefore call on you to immediately suspend David Coburn while you investigate this matter and if he is indeed found guilty of making these remarks then I expect he will be expelled from Ukip."
The First Minister said: "This is an appalling and reprehensible thing to say. For David Coburn to effectively compare Humza to a convicted terrorist because he is Muslim is disgraceful and he must surely face consequences for that.
"This is about the most basic standards of decency in public life - even for a party like Ukip - but there seems to be no depths below which Mr Coburn will not sink. Nigel Farage should remove him from his party."
Thackeray said: "This is a non-story. David Coburn did not compare Humza Yousaf to convicted terrorist Abu Hamza. He simply got a name wrong, which many people do on a daily basis. For example, I very often get referred to as Minty, which I believe is a character from EastEnders, but I don't take offence at that and run greeting to the papers about Mistyphobia.
"I just accept that sometimes people get a name wrong. It simply was a slip of the tongue."
The pair have clashed in the past - including this memorable zinger from Yousaf.
@HumzaYousaf You are a British citizen - never forget that— David Coburn MEP (@DavidCoburnUKip) January 21, 2015
@HumzaYousaf I don't seem to remember an EU symbol on my Passport- I do remember a British one though— David Coburn MEP (@DavidCoburnUKip) January 21, 2015
Radical cleric Hamza was sentenced to life in prison for a string of terrorism offences by a judge in New York in January.
Last year a jury found him guilty of supporting terrorist organisations, including aiding the taking of hostages in Yemen and seeking to set up an al Qaida training camp in the United States.
Hamza, previously from north London, was jailed in the UK for seven years for soliciting murder and inciting racial hatred in 2006 and first faced an extradition request from the US in 2004.
The Muslim Council of Scotland (MCS) has joined the calls for Coburn to resign as an MEP. Spokesman Mazhar Khan said: "MCS is appalled at the Ukip leader in Scotland, David Coburn, for his deeply offensive remark at Humza Yousaf MSP in referring to him as "Abu Hamza".
"The stereotyping of Muslims as extremists and terrorists, is one the most shameful forms of Islamophobia, and a manner constantly used by right-wing groups such as the BNP and the English/ Scottish Defence League at caricaturing Muslims. For a leader of a political party to make the same type of insult, is frankly disgraceful and reprehensible.
"The fact that Ukip is no stranger to such controversy and has regularly been accused of having racists within its ranks, only exacerbates the offence.
"To prove its rejection of intolerance and Islamophobia, MCS calls on Ukip leader Nigel Farage to do the right thing and take immediate action against David Coburn, such a person is not fit to represent Scottish people in the European parliament."
Scottish Labour leader Jim Murphy said the comments were "sickening and senseless".
"This isn't the first time that Mr Coburn has been caught out for having vile views," he added. "People across Scotland, including even those who voted for him, will now want to see the back of him."