Newspapers of all persuasions underlined the limited relief from crippling Western economic sanctions that Tehran was likely to secure in any agreement struck in Geneva.
But where reformist commentators talked up the "historic" nature of any deal involving the United States after more than three decades of hostility, conservative newspapers warned Iran's negotiators against being strong-armed into accepting a token easing of Western sanctions in return for a deal.
"Is it negotiation or blackmail by Washington?" asked the leading hardline daily Kayhan, under the front-page headline "Geneva agreement mirage".
"The Iranian negotiating team should aim for decisive action to lift the sanctions."
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For fellow hardline newspaper Vatan-Emrooz, all that was on offer to Iran's negotiators in Geneva was "Swiss chocolates" -- its front-page headline.
The leading reformist daily Shargh by contrast carried a front-page photograph of Foreign Minister Mohammad Javad Zarif standing alongside EU foreign affairs chief Catherine Ashton, all smiles, under the headline: "On the verge of a historic deal."
"Geneva is a historic event because Iran and the West have agreed to look each other in the eye after 35 years of mutual distrust and recriminations."
Other reformist titles played up the "shock" progress in the talks, and the "unexpected" meeting between Zarif and US Secretary of State John Kerry who curtailed a Middle East tour to join the talks yesterday.
But even moderate commentators warned against "excessive hopes" of relief from the Western sanctions that have crippled Iran's oil and banking sectors.
The negotiations stretched into an unscheduled third day today in the drive for a deal, with Russian Foreign Minister Sergei Lavrov flying in to join his Western counterparts.