The European Union coordinator for Iran nuclear talks, Enrique Mora, will travel to Tehran on Saturday to discuss unresolved issues, he tweeted late Friday.

“Travelling to Tehran tomorrow to meet Bagheri Kani. Working on closing the remaining gaps in the Vienna talks on the JCPOA. We must conclude this negotiation. Much is at stake,” Mora said.

The nuclear talks that started almost one year ago in Vienna ended inconclusively earlier in March, after Russia demanded exemption from Ukraine sanctions in its dealings with Iran. However, there are still unresolved issues between Tehran and Washington.

Iran is reportedly demanding that the United States remove the Revolutionary Guard, IRGC, from its terrorism list and the Biden Administration appears hesitant.

The prospect of such a move has galvanized opposition among US lawmakers, especially Republicans, who were skeptical or opposed to the revival of the 2015 nuclear agreement, JCPOA. Former president Donald Trump withdrew from the agreement arguing that it will not stop Iran from acquiring nuclear weapons.

US National Security advisor Jake Sullivan travelling in Europe said on Friday that if diplomacy with Iran fails, Washington is ready to increase pressure on Tehran in coordination with its European allies.

As the current stalemate continues, Iran-backed Houthi forces in Yemen launched drone and missile attacks against oil installations in Saudi Arabia on Friday, causing damage.