Talks aimed at saving the agreement with Iran on its nuclear program continued in Vienna on Monday, with Iranian officials expressing cautious optimism.

The talks were proceeding initially in bilateral format, people close to the talks said. They added that a meeting of the so-called Joint Commission of the political directors was expected in the course of the week.

Tehran Foreign Ministry spokesperson Saeed Khatibzadeh said good progress had been made in the last round concerning the lifting of sanctions and guarantees that the United States would not again withdraw from the agreement.

Once that had been agreed, Iran would once again stick to its technical obligations under the deal. "That is our aim, and we will not permit any deadlines to be set in this regard," the spokesperson said.

He added that a solution was possible in the near term: The U.S. had simply to return to the deal first hammered out in 2015 and lift its sanctions.

In 2018, the U.S. walked away from the agreement aimed at preventing Iran from constructing nuclear weapons, while permitting the peaceful use of nuclear power.

After the U.S. imposed stringent sanctions, Iran began breaking the agreement's provisions step by step, taking its capacity for constructing a nuclear weapon further.

Israel has repeatedly stated that it reserves the right to take military action to prevent the Islamic republic from possessing nuclear weapons.