Scottish Labour has declared itself firmly behind banning unconventional extraction of oil and gas.
Ms Sturgeon pointed to an ongoing moratorium on the technique while detailed research is carried out.
Green campaigners say the moratorium is "not the same as a permanent ban" and want parties to declare their stances.
Labour has been pushing for the SNP to make its policy on fracking clear before May's Scottish elections.
Energy minister Fergus Ewing told MSPs the government was taking a "cautious, evidence-led" approach, saying it would look at the evidence first and decide its position on hydraulic fracturing thereafter.
Delegates at the SNP's 2015 autumn conference narrowly voted down calls for the party to strengthen its position on fracking towards an outright ban.
During first minister's questions, Labour leader Kezia Dugdale pressed Ms Sturgeon on whether her opposition was "a real promise, or just an election pledge."
Ms Sturgeon replied: "We will not allow fracking in Scotland because we will not take risks with our environment while there are still unanswered questions.
"That's why we have a moratorium in place. That's the responsible way of proceeding."
Ms Dugdale quoted Ineos boss Jim Ratcliffe, who reportedly said he was told in private that the SNP is "not opposed" to fracking.
Ms Sturgeon repeated her comments about the moratorium, saying this means "it ain't allowed to happen", but would not be drawn on whether she supports an outright ban.
Her spokesman later said the first minister was "highly sceptical" about the technique, but said that "unlike Kezia Dugdale, we will continue to be led by the evidence".
Ms Dugdale suggested that despite the SNP's "temporary freeze" on fracking, they were going to "do it anyway".
She said: "Scottish Labour will go into the election with a very clear manifesto commitment - we will oppose fracking.
"A moratorium is not an outright ban; it's only a temporary stoppage.
"Her maybes aye, maybes naw response can only mean one thing - Nicola Sturgeon plans to give the green light if she is re-elected in May."
Ms Dugdale has been backed by the charity WWF Scotland and the Scottish Green Party.
WWF Scotland director Lang Banks said: "The Scottish government's current moratorium on fracking is not the same as a permanent ban, as we've consistently called for it to become.
"As we fast approach the Scottish elections, we need to hear from each of Scotland's parties on how they plan to deliver on their promise to cut emissions and secure the benefits of a low-carbon Scotland."
Scottish Greens co-convener Patrick Harvie said Labour's "sudden conversion" to opposing fracking was welcome.
He said: "Pressure from the Scottish Greens led first to a moratorium on fracking, then extended it to other dangerous methods of unconventional gas extraction.
"We remain determined to keep up the pressure for a full, permanent ban."
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Nicola Sturgeon has insisted "there will be no fracking" as Labour claimed the SNP were preparing to "give the green light" to the technique.