Sen. Tim Scott (R-S.C.), the top Republican on the Senate Banking Committee, this week called for Yellen to testify on the release of the $6 billion.

“The Senate should also investigate what led the Biden administration to allow a transfer of $6 billion to Iran and how it could expect Iran to not use that money to continue to fuel terrorism,” Scott said.

Yellen said the funds were made available solely for humanitarian purposes, such as food and medicine.

“These funds have not been touched,” she said.

The Biden administration has previously said it has the power to refreeze the funds, which were released after the U.S. waived sanctions allowing banks to convert the money that had been blocked in South Korea and transfer it to Qatar’s central bank.

Yellen also said the U.S. has “not in any way” relaxed sanctions on Iranian oil.

“We have sanctions on Hamas, on Hizbollah,” she said. “This is something we’ve been constantly looking at, and using information that comes available to tighten sanctions, we will continue to do that.”

Paola Tamma contributed to this story.