Iranian President Hassan Rouhani has said his country is "serious" about negotiations on a comprehensive nuclear deal with world powers, a week before a fresh round of talks.
However, Deputy Foreign Minister Abbas Araqchi said on Monday that "the defence-related issues were a red line for Iran".
Negotiations are set to resume in Vienna on February 18 and 19 between Iran and the so-called P5+1 - Britain, France, the United States, Russia and China plus Germany.
Iran is ready to enter negotiations with the P5+1 (group of world powers) to reach a comprehensive and final agreement
"Iran is ready to enter negotiations with the P5+1 (group of world powers) to reach a comprehensive and final agreement," Rouhani told Tehran-based foreign diplomats in remarks broadcast live on state television.
"We are serious in this regard, as we were serious in the first step," he said referring to three rounds of intensive negotiations last year that culminated in a landmark, interim deal on November 24.
Building on the November deal, negotiators hope to eventually reach a comprehensive accord to allay international concerns that Iran is pursuing nuclear weapons capability, allegations denied by Tehran.
Rouhani's remarks came a day after Iran and the UN nuclear watchdog struck a seven-step deal in separate but parallel negotiations that seek to enhance transparency over Tehran's nuclear work.
That deal included a promise by Iran to clarify its use of detonators as part of a probe into long-standing allegations that its past nuclear work, mostly before 2003, had "possible military dimensions".
The US lead negotiator in the talks, Wendy Sherman, last week told a Senate hearing that Iran's ballistic missile programme would be addressed in the comprehensive deal.
New missiles tested
The missile programme - targeted by UN Security Council sanctions - worries Western powers, as Iran boasts long-range missiles with a maximum range of 2,000km, enough to reach Israel.
But Araqchi, who is also a senior Iranian nuclear negotiator, said that the ballistic missile programme would not be up for negotiation.
"We will not allow such issues to be discussed in future talks," he said.
On Monday, the official IRNA news agency reported that Iran had "successfully tested" two missiles on the eve of the 35th anniversary of its Islamic revolution.
"The new generation of ballistic missile with a fragmentation warhead, and a Bina laser-guided surface-to-surface and air-to-surface missile, have been successfully tested," Defence Minister Hossein Dehgan said, according to AFP news agency.
Foreign Minister Mohammad Javad Zarif, Iran's top negotiator, said that the talks in Vienna would be "difficult," while anticipating that a framework for future negotiations would be discussed.
"The biggest challenge is the lack of trust," he added.
Under the interim accord, Iran agreed to temporarily cap parts of its nuclear activities in exchange for modest relief from crippling international sanctions.
The Western powers also promised that new sanctions would not be imposed against it during the six-month duration of the interim deal, which came into effect on January 20.