Maj. Gen. Mohammad Ali Jafari was quoted by Iran's semiofficial Fars News Agency as saying the Iranian government entered nuclear negotiations with "heroic flexibility" but "we cannot be optimistic."
Members of the P5-plus-1 -- Britain, China, France, Russia and the United States, plus Germany -- met Tuesday with their Iranian counterparts in Vienna to discuss Iran's nuclear program. Prospects were dimmed by expressions of frustration from both sides.
The U.S. State Department said Monday securing an agreement with Iran on its nuclear program "will be tough" and the road ahead will have "some ups and probably many downs."
The Iranian government expressed frustration with a U.S. position that a military option is on the table if Iran goes back on an agreement to curb its nuclear research activity in exchange for relief from some economic sanctions.
Iran is suspected of pursuing technology needed to develop a nuclear weapon, an allegation it denies.
Notable deaths of 2014 [PHOTOS]