(AP) — World powers have held a fourth round of high-level talks aimed at bringing the United States back into a landmark nuclear deal with Iran. Both sides suggested a resolution was possible but major stumbling blocks remain. A Russian delegate tweeted following Friday’s meeting that “the participants agreed on the need to intensify the process” and appeared ready to “stay in Vienna “as long as necessary to achieve that goal. Former President Donald Trump pulled the U.S. out of the deal in 2018. Iran reacted by steadily increasing violations of the deal. U.S. President Joe Biden has said he wants to rejoin the deal but that Iran needs to return to compliance with the accord.