Mohammad Javad Zarif held private talks with counterparts from Germany and France, before meeting with a group of EU leaders on the sidelines of a meeting of top EU diplomats in Luxembourg.
Zarif predicted intense and difficult days ahead before the deadline to strike a deal with world powers over Tehran's nuclear programme.
British Foreign Secretary Philip Hammond, who also met with Zarif, said diplomats are "going to pull all the stops out" to reach an agreement by the deadline.