EU nuclear expert Stephan Klement met with Iranian officials in Istanbul on Iran's nuclear program.
EU policy experts "provided further details on the revised confidence-building proposal put forward to Iran" during February meetings in Kazakhstan, Mann said in a statement.
Negotiations between Iran, the five permanent members of the U.N. Security Council and Germany are scheduled for April in Kazakhstan.
Iran is suspected of pursuing the technology needed to manufacture a nuclear weapon, an allegation Tehran denies. The government described last month's multilateral nuclear negotiations in Kazakhstan as positive, though no breakthroughs were announced.
The statement from Mann provided few details about the proposals. No indication of Iran's reaction to the Istanbul meetings was given.
U.S. President Barack Obama issued a statement to Iran on the occasion of Nowruz, the Iranian New Year.
"Now is the time for the Iranian government to take immediate and meaningful steps to reduce tensions and work toward an enduring, long-term settlement of the nuclear issue," Obama said.