Brexit: Scotland to declare independence if Britain votes to leave EU, says Nicola Sturgeon
Read More: British Prime Minister sets June 23 date for Britain's in/out EU referendum
"Across the UK the polls suggest this campaign is on a knife-edge and that's why I think it's important for the in-campaign to be positive," Sturgeon said.
The Scottish vote, which is about 5 million, however is dwarfed by that of England which represents about 84 pc of the population of the United Kingdom.
Read More: Irish workers in UK will not be affected by EU reform bid - Kenny
"If we get into the situation, where Scotland votes to stay in, the rest of the UK votes to come out, then people in Scotland will have big questions they will want to look at again about whether Scotland should be independent."
Scots rejected independence by 55-45 pc in a vote in 2014 but since then the SNP has gained further strength, taking 56 of the 59 seats representing Scotland in the national parliament in London in last May's election.
Mr Cameron has come out in favour of the UK remaining in the EU, saying that he had securing a deal from other EU leaders that would give Britain "a special place within Europe".
Read More: Merkel: British EU demands are 'justified' and 'necessary'
Former SNP leader Alex Salmond said he did not rate the EU deal that Cameron had secured.
If "we were dragged out against our will by the votes of a much larger English (electorate), then the pressure for another independence referendum in Scotland would be irresistible and I think very rapid," Mr Salmond said.