First Vice Foreign Minister Choi Jong-kun is in Vienna this week for talks with negotiators from the U.S. and five other countries in the Iran nuclear deal, to seek ways to resolve Iran's frozen assets in South Korean banks.

While South Korea is not a party to the Joint Comprehensive Plan of Action(JCPOA), it has closely communicated with the involved countries about returning to the nuclear deal following the 2018 U.S. withdrawal.

About seven billion dollars worth of Iranian assets remain frozen in two South Korean banks under U.S. sanctions imposed following its withdrawal from the deal.

Amid ongoing negotiations for the return, U.S. State Department spokesperson Ned Price said on Tuesday that, while sanctions relief is at the heart of the negotiations, "nothing is agreed until everything is agreed."

The spokesperson said despite some progress, an agreement has yet to be reached on Tehran's return and sanctions relief.