About 90 percent of the work on the Iran nuclear deal has been done, but the 10 percent that remains might prove a tough nut to crack. That’s according to the permanent representative of Russia at Vienna international organizations.

In an interview for Russian business daily Kommersant, Mikhail Ulyanov said that some politically sensitive issues remain and have yet to be settled by the negotiators. This includes the question of whether the United States could again pull out of the deal under different leadership.

Ulyanov noted that the U.S. side had said it could not provide guarantees that would not happen because of its legislation. According to him, however, the guarantee is pretty obvious: if one side, he said, begins to “misbehave”, the other side would have the right to respond in kind. For instance, if the United States were to pull out of the deal, Iran would recommence enriching uranium.

Ulyanov declined to name other examples of the politically sensitive issues that are holding the deal back but noted that right now there is no clarity even about when the negotiations would resume. Iran, he said, is settling in under new leadership after the June elections; even the Iranians don’t know when the negotiations might resume. This is naturally annoying for the other sides on the negotiations table, Ulyanov added.

This situation led the United States and France to warn Iran against drawing out the negotiations, with Radio Free Europe citing unnamed diplomats as saying that the negotiations could deteriorate unless Iran granted an extension to the International Atomic Energy Agency’s permit to monitor nuclear activities.

This extension has yet to take place.

This is the latest sign that Iran’s return to international oil markets would be tougher than it looked at the start of negotiations. It would be tougher still under the new hardline Iranian leadership.