His comments came after Iran and six world powers - Britain, China, France, Russia, the US and Germany - ended a fourth round of nuclear talks in Vienna with little progress to report, Xinhua reported.
Iran says its nuclear energy programme is for peaceful purposes.
"Agreement is possible. But illusions need to go. Opportunity shouldn't be missed again," Zarif said on Twitter.
On 20 July, an interim deal, under which Iran curb uranium enrichment in return for the lifting of some Western sanctions, is due to expire.