If the U.S. is serious about rejoining the 2015 nuclear accord, “then a serious indication is needed,” says Iran’s foreign minister.

Iranian Foreign Minister Hossein Amir-Abdollahain said on Saturday that the Islamic Republic had requested that the United States unfreeze “at least” $10 billion in frozen Iranian funds to prove it was serious about rejoining the 2015 Joint Comprehensive Plan of Action.

In an interview with Iranian state television, Amir-Abdollahian said that U.S. officials had attempted to contact the Iranian government last month at the United Nations General Assembly in New York about restarting the stalled nuclear talks in Vienna.

“The Americans tried to contact us through various channels [at the UNGA] in New York, and I told the mediators if America’s intentions are serious then a serious indication was needed … by releasing at least $10 billion of blocked money,” he said.

The sixth round of negotiations in Vienna over a possible return to the JCPOA wrapped up in June, and no date has yet been set for a seventh-round of talks. Iran held presidential elections on June 18 and has argued that it needs more time to settle in the new government before returning to the nuclear talks.

U.S. Special Representative to Iran Robert Malley told Bloomberg TV in an interview that aired on Sept. 3 that while the United States was prepared to be patient with Tehran with regard to negotiations about a return to the 2015 Joint Comprehensive Plan of Action, it “can’t wait forever.”

Malley said that while Iran’s request for more time was understandable, its rapidly advancing nuclear program could render additional negotiations pointless.

Amir-Abdollahian reiterated on Saturday that Iran would “soon” return to the stalled nuclear talks in Vienna, but declined to give a date.