Zarif traveled to Pakistan to meet with regional delegates gathered for a regular summit of the Developing 8 -- Bangladesh, Egypt, Indonesia, Iran, Malaysia, Nigeria, Pakistan, and Turkey.
Zarif said he was frustrated some members of the multilateral negotiating team hammering out a deal on Iran's nuclear program didn't seem sincere.
"We have to understand that talks are dealing with a difficult issue that can be sorted out with close cooperation of both sides," he told the official Islamic Republic News Agency. "We hope that the other party would continue the dialogue with Iran sincerely and observe its commitment."
Zarif didn't say which party lacked sincerity.
Members of the Western community have said they're committed to enforcing existing sanctions on Iran. Iranian negotiators said any new sanctions could undermine the spirit of a deal reached last month in Geneva, Switzerland.
Under the terms of the interim deal, Iran agreed to curb some of its nuclear enrichment activity in exchange for relief from some economic sanctions.
Iranian nuclear officials said this week enrichment of uranium to 20 percent purity, seen as a breakthrough for a nuclear weapon, could resume quickly if negotiations collapse.