South Korea and Iran have held working-level talks on resuming imports of Iranian crude oil and unfreezing Iranian funds held in the East Asian nation, South Korea's Foreign Ministry said on Wednesday.

South Korea was previously one of Iran's leading Asian oil customers. The move comes as negotiations to revive Tehran's nuclear agreement with world powers resumed in Vienna.

"Our side expressed hope for the resolution of issues related to sanctions such as the transfer of frozen funds upon the agreement on the restoration of the Joint Comprehensive Plan of Action (JCPOA) now underway in Vienna," the release said.

The Iranian side stressed the importance of an early resolution of the matter of the frozen funds, it added. Iranian officials could not immediately be reached for comment.

Iran and South Korea are also discussing the trading of crude oil and oil products, on the condition sanctions are lifted as progress is made in nuclear negotiations, the release said.

Previously South Korean oil buyers chiefly imported condensate, or an ultra-light form of crude oil, from Iran.

The United States reimposed sanctions on Iran in 2018 after then-President Donald Trump withdrew from Tehran's 2015 nuclear agreement with six major powers, under which it agreed to curb its nuclear program in exchange for U.S. sanctions relief.

Tehran has repeatedly demanded the release of about $7 billion of its funds frozen in South Korean banks under U.S. sanctions, saying Seoul was holding the money "hostage."

South Korea, the world's fifth-largest crude buyer, imported a total of 12.6 million tons of crude in January against 10.3 million tons a year ago, preliminary data from the Korea Customs Service showed on Tuesday.