Major world powers have quietly begun talks on a UN Security Council resolution to lift UN sanctions on Iran if a nuclear agreement is struck, Western officials said Thursday, according to the Reuters news agency.

The comments come a day after U.S. Secretary of State John Kerry told Congress that an Iran nuclear deal would not be legally binding, meaning future presidents could decide not to implement it.

But a Security Council resolution on a nuclear deal with Iran could be legally binding, say Western diplomatic officials, complicating and possibly undercutting future attempts by Republicans in Washington to unravel an agreement, noted Reuters.

Iran and the six world powers are trying to turn an interim 2013 deal into a permanent agreement.

Under the interim deal, Iran committed to limit its uranium enrichment to five percent and is gradually winning access to $4.2 billion of its oil revenues frozen abroad and some other sanctions relief.

Talks to reach a permanent deal have continuously stalled and two deadlines for a final deal have been missed, with a third one looming on July 1 and an initial deal needing to be worked out by March 31.

So far, those talks have focused heavily on separate U.S. and EU sanctions on Iran’s energy and financial sectors, which Tehran desperately wants removed and are a sticking point in the talks that resume next week in Lausanne, Switzerland.

Western officials involved in the negotiations told Reuters, however, that they are also discussing a draft resolution for the 15-nation Security Council to begin easing UN nuclear-related sanctions that have been in place since December 2006.

“If there’s a nuclear deal, and that’s still a big ‘if’, we’ll want to move quickly on the U.N. sanctions issue,” an official said, requesting anonymity.