Talks will resume next week on the future of Iran's nuclear program with the goal of beginning to draft a comprehensive agreement in May, a senior Obama administration official said on Friday.

The next round of negotiations will seek to build on the work that has been done since January, when an interim deal between Iran and the five permanent members of the U.N. Security Council took effect.

That deal eased some economic sanctions in return for Iran rolling back parts of its nuclear program, which the United States and others believe is designed to produce a weapon. Iran says its nuclear intentions are peaceful.

While officials in Washington are optimistic that negotiations are progressing on track, a number of significant potential roadblocks need to be worked through if a long-term agreement is to be reached.

These include determining what will happen to Iran's heavy water reactor in Arak, which the United States and its allies would like to see neutralized. That is a sticking point for Tehran.

"We know where the gaps are that have to be bridged," the official told reporters, adding that the United States remains clear-eyed about Iran's motivations.

New concerns have also been raised over reports that Russia is laying the groundwork for an oil-for-goods deal with Iran, which could violate the terms of the interim agreement and derail future talks.

According to the official, the reports are being taken seriously but are not yet having a substantive impact on negotiations.

The administration has communicated to all parties that violating limits on Iran's oil exports could trigger new economic sanctions.

This development comes less than three weeks after the United States and the European Union enacted a series of sanctions targeting Russian officials, in response to Russia's annexation of Crimea.

(CNN) --