Iranian Foreign Minister Hossein Amir Abdollahian called on the American side to take what he described as the right way to achieve the nuclear agreement, instead of playing with time and words.
In a press conference in the Lebanese capital, Beirut, on Thursday, Abdullahian welcomed the return of relations with Saudi Arabia, but indicated that Tehran was receiving contradictory messages from Riyadh.
The Iranian minister said that reaching an agreement on his country's nuclear program could happen at any time if Washington adopted a realistic view of things, he said, noting that the issue of lifting sanctions on Tehran had not been fully settled.
But Abdullahian warned that Tehran's readiness for what he described as a good, strong and stable agreement will not be at the expense of Iran's red lines, according to him, stressing that "any final nuclear agreement will benefit the peoples of the region."
During a visit to Damascus on Wednesday, Abdullahian said that his country and world powers were closer than ever to reaching an agreement in Vienna.
But US officials were more cautious in their assessment of efforts to revive the 2015 agreement, which limits Iran's nuclear program in return for the lifting of economic sanctions imposed on it.
US National Security Adviser Jake Sullivan said Wednesday that the United States and its allies had made progress in the Iran nuclear talks, but that problems remained, and it was not clear if they would be resolved.
The talks in Vienna, in their latest round, came close to reaching an agreement when Russia made last-minute demands to the United States and insisted on guarantees that sanctions imposed on Moscow over its war on Ukraine would not harm its trade with Iran.
Relations with Saudi Arabia
On another subject, during the same press conference in Beirut, the Iranian minister said that Tehran welcomes the return of bilateral relations with Saudi Arabia, "but so far it has received mixed messages from the kingdom. We expect the Saudis to act in the interest of the region."
Saudi Arabia and Iran began direct talks last year in an attempt to contain tension between the two countries.
The Iraqi Foreign Minister - who is mediating the talks between the two parties in Baghdad - had previously said that the fifth round would be held on March 16, but the Iranian Nour News Agency said that Tehran "unilaterally suspended the talks with Saudi Arabia" without giving the reason.