Nigel Farage has defended a Ukip poster showing a huge queue of non-white migrants on the borders of the European Union after it was branded "disgusting".
The Eurosceptic leader denied that the people shown, who were crossing between Croatia and Slovenia to a refugee camp, were desperately fleeing terror in Syria.
Dismissing suggestions that the poster was racist and exploited human misery, he insisted very few people who came into Europe last year would qualify as genuine refugees.
But Scotland's First Minister Nicola Sturgeon said: "This is disgusting."
Mr Farage launched the poster with a battlebus tour through Westminster followed by 10 vans plastered with the image.
Islamic State (IS, also known as Isis) are exploiting the migrant crisis to flood the continent with terrorists, he claimed.
"This is a photograph, an accurate, un-doctored photograph, taken on October 15 last year following Angela Merkel's call in the summer and, frankly, if you believe, as I have always believed, that we should open our hearts to genuine refugees, that's one thing," Mr Farage said.
"But, frankly, as you can see from this picture, most of the people coming are young males and, yes, they may be coming from countries that are not in a very happy state, they may be coming from places that are poorer than us, but the EU has made a fundamental error that risks the security of everybody."
Told the people were refugees, he said: "You don't know that - they are coming from all over the world.
"If you get back to the Geneva Convention definition, you will find very few people that came into Europe last year would actually qualify as genuine refugees."
He added: "We have just had, in the last two weeks, the Dusseldorf bomb plot has been uncovered - a very, very worrying plan for mass attacks along the style of Paris or Brussels. All of those people came into Germany last year posing as refugees.
"When Isis say they will use the migrant crisis to flood the continent with their jihadi terrorists they probably mean it."
Mr Farage said he was "feeling better about things than I was two weeks ago" about the prospect of victory for the Leave campaign.
"The Leave side now really are in with a very serious chance," he added.
"For years I have been considered some sort of nutcase who thinks we should leave the European Union and that nobody decent or respectable would ever take that view and now we have people like (Michael) Gove and Boris (Johnson) and people on the Labour side as well so, of course, I have welcomed all of them."
The Ukip leader said the Leave campaign would "maybe" have even stronger polling if they had worked together.
"I've not squabbled with anybody. I have said for a year I will work with anybody, from left, centre and right."