David Cameron has said voting to stay in the European Union does not make you "less patriotic" as he continues to try to persuade Britain to stay.
His comments come as the referendum debate becomes increasingly bitter, with Iain Duncan Smith accusing the Remain camp of using "spin, smears and threats" that will haunt them beyond the vote.
The Prime Minister hit back at claims Britain will be more powerful outside the EU, and insisted voters can retain their patriotism while voting to Remain.
In a speech to the Scottish Conservative conference in Edinburgh, he said the UK is "stronger in a reformed Europe, too".
Mr Cameron said: "Our membership helps put Scotland in the driving seat on the world's biggest issues, and on this, Scotland proves something important.
"It shows that you can be a strong, successful, proud Scot - and be part of the United Kingdom and European Union.
"Being in these two clubs doesn't diminish Scotland's identity. It doesn't make you less of a Scot, or less patriotic.
"What matters is turning patriotism into action, being able to get things done for the country you love. I believe that's what we can do in a reformed Europe."
The Prime Minister said being part of a reformed EU offered the "best of both worlds" - access to the single market but without the unpopular aspects of the European project such as the euro.
Government officials have warned Brexit would usher in a period of economic uncertainty that could lead to job losses and price hikes.
But the Leave camp have accused their opponents of launching "project fear" and trying to scare the electorate into voting to stay.
As the war of words between the two campaigns escalates, Mr Duncan Smith, the Work and Pensions Secretary, said he found the acrimony between the factions "troubling".
The Brexit-backer accused rivals of using "desperate and unsubstantiated claims" and peddling a "nightmare" image of Britain's chances outside the EU, with "biblical consequences".
Writing in The Daily Mail, he wrote: "The Remain campaign's case seems almost wholly based on what they describe as the nightmare of leaving.
"This case has in whole or in part become characterised by spin, smears and threats ... In the last fortnight we have had a series of highly questionable dossiers - threatening almost biblical consequences if we dare to consider a future outside of the European Union.
"We've seen a series of stunts, whereby big businesses, big banks, and powerful politicians from other EU member states seek to bully the British people into believing their jobs and security are at risk."
He made the comments after French president Francois Hollande warned of the "consequences in many areas" should Britain choose to leave the EU.
Mr Duncan Smith warned against painting Eurosceptic thinking as "heretical and dangerous" and expressed fears over the after-effects of an embittered referendum campaign.
He wrote: "The acrimonious manner in which all this has been conducted is troubling, and will I fear have consequences long beyond June 23.
"After all, such desperate and unsubstantiated claims are now being made that they begin to damage the very integrity of those who make them in the eyes of the public."
His view was echoed by Eurosceptic Conservative MP Dr Liam Fox, who told the BBC Radio 4 Today Programme the sour tone of the referendum debate risked making it harder for Conservative Party MPs to unite again after the vote.
He said: "How easy or how hard it is for us to come together and govern this country as a majority party is largely dependent on how well we treat one another, and the respect with which we treat one another, in the run up to the referendum."