A delegation from the International Atomic Energy Agency (IAEA) arrived early Wednesday in Tehran for new talks on Iran's disputed nuclear programme, the news agency Isna reported.
The UN nuclear watchdog will work hard to resolve differences with Iran over its nuclear programme at the talks, the body's chief inspector, Herman Nackaerts, told reporters at Vienna airport on Tuesday.
"Differences remain... we will work hard to try to resolve these differences," Nackaerts said as he boarded a plane for Tehran. "We will have good negotiations."
The IAEA delegation are due to meet Iranian officials on Wednesday for the eighth round of talks in a year, and the third such trip in the past three months.
The IAEA wants Iran to grant it access to nuclear sites, particularly Parchin, as well as people and documents that can help provide information on its November 2011 report into Tehran's nuclear activities.
In the report, the IAEA said it had credible information that Iran had worked to develop nuclear weapons before 2003 and possibly again since then.
Tehran insists that its nuclear programme is for peaceful purposes.
The IAEA believes that activity relevant to nuclear weapons development took place at the Parchin military base near Tehran.
The Islamic republic says the IAEA already visited Parchin twice in 2005 and found nothing untoward. The agency however has countered that new information obtained since then makes it want to go back.
The IAEA also says that because of activity at Parchin spotted by satellite, including moving "considerable" volumes of earth, its inspections there will be "seriously undermined" if it ever goes.
As a signatory of the NPT, Iran has to submit its nuclear facilities to inspection by the agency, but insists that Parchin is a military site and therefore not subject to the inspection.
Iran's foreign ministry spokesman Ramin Mehmanparast hinted Tuesday that inspection of the Parchin military site by the IAEA would be possible in the context of a "comprehensive agreement" that recognises its right to peaceful nuclear energy.