A top official in Iran says the Islamic Republic has written back in response to letters sent by U.S. President Barack Obama, the first acknowledgement of such correspondence.

The letter writing is part of a recent thaw in relations between the two countries since the 1979 Islamic Revolution and the storming of the U.S. Embassy in Tehran, where 52 Americans were held hostage for more than a year.

But it isn't clear whether Supreme Leader Ayatollah Ali Khamenei himself responded to Obama's letters.

Ali Shamkhani, the secretary of Iran's Supreme National Security Council, made the announcement on Iranian state television Wednesday night. Shamkhani said the most recent letter dealt with issues pertaining to Iran's contested nuclear program. Iran and world powers are negotiating a final deal regarding it now.