Nicola Sturgeon voices 'concern' over early EU referendum
Scotland's First Minister Nicola Sturgeon said she was "increasingly concerned" about the possibility of an early EU referendum.
Some reports have suggested the prime minister, David Cameron, could call the vote in June.
Ms Sturgeon said a "longer period" might be needed for a campaign for continued UK membership.
The Conservative MSP, Alex Johnstone, said there would be "enough time" for people to make an informed decision.
- A guide to the UK's planned in-out EU referendum
- Q&A: What Britain wants from Europe
- Who's who guide to the 'UK out' campaigns
- Who's who guide to the 'UK in' campaigns
Mr Cameron is seeking to renegotiate the terms of UK membership with other EU leaders before calling the "in/out" referendum.
At the weekend, he said he was "hopeful" of reaching a deal with other EU leaders in February and that the referendum "would follow".
He has previously committed to holding the ballot before the end of 2017.
Ms Sturgeon said she wanted the UK to remain in the EU, even though she believed a vote to leave could hasten another referendum on Scottish independence.
She urged Mr Cameron to get away from "a very narrow focus" on renegotiation issues and "get out there" to make the case for continued membership.
Otherwise she said he would lose ground to the leave campaign and be guilty of a "failure of leadership".
A Downing Street source said the debate over the UK's future relationship with the EU could not properly begin until renegotiation was completed.
Tory MSP Alex Johnstone said: "It's important that this [the EU referendum] is done quickly and that the referendum takes place as soon as we have a deal on the table.
"There will be time, there will be opportunity for people to look at that deal and consider it.
"But that can take a month or two months. It doesn't take two years.
"It's certainly enough time for people to judge the deal and for people to make an informed decision," he said.
A Scottish Labour spokesperson said: "It's essential that as many people as possible have their say."