Washington is prepared to walk away from nuclear negotiations in Vienna if Iran displays intransigence, State Department spokesperson Ned Price said on Monday.

“We are prepared to walk away if Iran displays an intransigence to making progress," Price told reporters at a regular press briefing of the indirect talks taking place in Vienna.

The United States and its allies and partners will pursue "alternatives" if Iran is "unwilling to engage in good faith," he added, without detailing those alternatives.

Reuters on Monday quoted two sources close to the talks in Vienna as saying that Iran had submitted new demands, while continuing to insist on existing ones, including the removal of a US foreign terrorist organization (FTO) designation against Iran's Revolutionary Guards (IRGC).

"Iran's stance after Bagheri's trip to Tehran has become even more uncompromising .... they now insist on removal of sanctions on the IRGC and want to open issues that had already been agreed," one of the sources said.

Tehran has been demanding the lifting of more sanctions than the US is willing to accept, including removing its Revolutionary Guard from the list of Foreign Terrorist Organizations. It also demands firm guarantees that in the future the US will not act contrary to the agreement.