Kerry, who is attending a three-day international investor conference in Egyptian resort town of Sharm el-Sheikh, said the purpose of these talks was "not just to get any deal, it is to get the right deal".
"We made some progress, but there are still some gaps, important gaps."
The Iranian nuclear talks are entering their critical end-game with Kerry due to meet his Iranian counterpart in Switzerland after the Sharm el-Sheikh conference ends.
The parties hope to reach a full accord by July 1.
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But Iran's supreme leader, Ayatollah Ali Khamenei, has criticised the negotiations, and is to give a closely watched Iranian New Year's address on March 21.
On Thursday Khamenei said the other side in the talks was "deceitful and stabs in the back," according to Iranian news agency ISNA.
Kerry will travel to the Swiss city of Lausanne tomorrow to meet Iranian Foreign Minister Mohammad Javad Zarif.