When they last met on July 19, Iran, the United States, Britain, France, Germany, Russia and China agreed to extend the deadline to reach a comprehensive agreement under which Iran would curb its nuclear activities in exchange for the easing of economic sanctions to Nov. 24 from July 20.
Announcing the talks in Washington on Wednesday, the State Department said Deputy Secretary of State Bill Burns would lead the US delegation, which also includes Under Secretary of State Wendy Sherman and Jake Sullivan, the national security adviser to Vice President Joe Biden.
Burns and Sullivan are expected to leave the Obama administration this year, Reuters reported.
Iran's state news agency IRNA said on Thursday the talks had started, with deputy Foreign Minister Abbas Araqchi leading the Iranian delegation.