An Iranian delegation broke off talks with six world powers over implementing a landmark nuclear deal to return to Tehran, Iran's news agency said Friday. The so-called expert-level delegates, meeting since Monday at the Vienna headquarters of U.N. nuclear watchdog International Atomic Energy Agency, halted the talks on enforcement mechanisms to return to Tehran for consultations, the official Islamic Republic News Agency said in a report monitored by United Press International. The report did not say why the delegation, led by Iranian Foreign Ministry political and legal affairs Director General Hamid Baeidinejad, suspended the talks Thursday night. Stephen Clement, leading the talks for EU foreign policy chief Catherine Ashton on behalf of the five permanent members of the U.N. Security Council plus Germany, had no immediate comment. The suspension of the talks came hours after the Obama administration, facing growing pressure from Congress to maintain or increase economic sanctions on Iran, blacklisted more than a dozen companies and individuals for allegedly helping Tehran evade international oil sanctions. At the same time, House and Senate lawmakers agreed Thursday not to vote on new sanctions this year, following a White House campaign to stall legislative action for at least six months while the United States, Britain, France, Russia, China and Germany negotiate a comprehensive deal over Tehran's nuclear program. Iranian Foreign Minister Javad Zarif told Time magazine in an interview published Monday any new sanctions would kill a comprehensive deal. The talks in the Austrian capital were part of an interim six-month deal reached Nov. 24 in Geneva, Switzerland, calling for Iran to halt production of near-weapons-grade nuclear fuel in exchange for some relief from economic sanctions amounting to $6 billion to $7 billion.