US Secretary of State John Kerry pauses as he delivers a statement on the Iran talks in Vienna, Austria, July 9, 2015. [Photo/Agencies]

TEHRAN - The United States pushed the nuclear talks into deadlock with excessive demands, local Fars news agency quoted an Iranian diplomat in Vienna as saying on Thursday.

Western parties of the talks, especially the United States, have raised excessive demands beyond previous agreements with Iran, the Iranian diplomat said on condition of anonymity, accusing the western parties of playing "blame game" to pin the responsibility of possible failure on Iran, according to the report.

Iranian Foreign Minister Mohammad Javad Zarif tweeted earlier that "we're working hard, but not rushed, to get the job done. Mark my words; you can't change horses in the middle of a stream."

Earlier in the day, US Secretary of State John Kerry said major powers will not be "rushed" into a nuclear deal with Iran, adding that he was prepared to walk away from the talks if "tough decisions" are not made soon.

Talks between Iran and five UN Security Council permanent members plus Germany have extended well into a second overtime after missing the deadlines of June 30 and July 7.