U.S. Secretary of State Hillary Clinton says the U.S. is prepared to hold bilateral talks with Iran on its nuclear program.

Reuters reports that Clinton told a group of officials, diplomats and experts from the U.S. and the Middle East on Friday in Washington that the disputes with Iran have been her biggest challenge.

The U.S. suspects Iran of wanting to develop nuclear arms but Iran has repeatedly stressed that it is not developing nuclear weapons and that its nuclear program is peaceful.

Clinton maintained that the U.S. is working with the 5+1 group to resume nuclear talks with Iran, adding: “We are working on the P5+1 and making our willingness known that we are ready to have a bilateral discussion if they are ever ready to engage.”

She added that the proposal being prepared by the world powers will “make it clear we are running out of time. We have got to get serious; here are issues we are willing to discuss with you, but we expect reciprocity."

In October, the New York Times reported that unidentified U.S. officials have indicated that Iran and the U.S. are coming to terms over entering bilateral talks over the nuclear issues. The report was later denied by the While House, while Ali Akbar Velayati, a former Iranian foreign minister considered to still be a close confidant of Iran’s Supreme Leader, announced that Iran’s policy against the U.S. has not changed.

Iranian Foreign Minister Ali Akbar Salehi said last month that the decision to hold talks with the U.S. can only be made by Ayatollah Khamenei.