NEW : Iran has been one of the biggest allies of Syrian President Bashar al-Assad , the man who U.S. President Barack Obama and other Western leaders have publicly said they want out of power -- even going so far as to support moderate opposition elements fighting to oust him . Iran President tweets on `` 1 hour of constructive & pragmatic dialogue '' NEW : He criticizes U.S.-led strikes in Syria , yet opens door to `` a new atmosphere '' with U.S. NEW : Cameron : Despite `` severe disagreements , '' Iranians could help defeat ISIS . NEW : Obama says he will not allow Iran nuclear program to continue without his approval --
NEW : Iran President tweets on `` 1 hour of constructive & pragmatic dialogue '' NEW : He criticizes U.S.-led strikes in Syria , yet opens door to `` a new atmosphere '' with U.S. NEW : Cameron : Despite `` severe disagreements , '' Iranians could help defeat ISIS . NEW : Obama says he will not allow Iran nuclear program to continue without his approval --