Inspectors from the International Atomic Energy Agency (IAEA) are due to hold talks in Tehran on January 16 on Iran's controversial nuclear program.
IAEA officials say they will press again for access to the Parchin military complex, southeast of Tehran.
The IAEA suspects Iran conducted explosive tests there with possible nuclear weapons applications.
Herman Nackaerts, deputy director-general of the International Atomic Energy Agency (IAEA), was hopeful before departing for Tehran.
"We hope that we will be allowed to go to Parchin. And if access is granted, we will welcome the chance to do so," he said. "And as you will have seen, we are ready to go."
So far, Iran has denied the IAEA access to Parchin. Tehran says the IAEA inspected Parchin in 2005 and found no evidence of secret nuclear work.
Satellite images taken last year indicate buildings have been demolished and soil removed at Parchin, erasing possible traces of illicit activity.
On the eve of the talks with the IAEA, Foreign Ministry spokesman Ramin Mehmanparast said Iran is ready to lift "any ambiguities" over its nuclear program, but he added Tehran wants the West to recognize its nuclear "rights," believed to include uranium enrichment.
Iran is already under four rounds of UN sanctions and Western oil and banking sanctions for its refusal to halt uranium enrichment, a technology that can be used not only to produce fuel but material for nuclear bombs as well.
A report this week by U.S. nonproliferation experts said Iran could produce enough weapons-grade uranium for one or more nuclear bombs by the middle of 2014 and urged Washington and its allies to strengthen sanctions on Iran.
Iran has repeatedly denied it is secretly developing nuclear weapons.
Mehmanparast said a religious decree, or fatwa, issued in 2005 by the country's leader, Ayatollah Ali Khamenei, banning nuclear weapons is binding for the Iranian government.
Analysts say world powers engaged in talks with Iran on ending the decade-old dispute over Iran's nuclear program will be watching the talks in Tehran for a sign of Iran's willingness to compromise.
The six powers -- the United States, France, Germany, China, Russia, and Britain -- are tentatively scheduled to meet again later in January.
With reporting by AP and Reuters