Iran's foreign minister said Wednesday that US President Barack Obama was 'responsible' for making sure that Washington respects a final agreement over Iran's nuclear programme even though Congress has been given a say on the accord's fate.

"It is the obligation of the government of the United States to implement its international agreements. And we will hold the US government, the US president accountable" for the application of the treaties that they sign, Mohammad Javad Zarif told journalists in Lisbon.

He was reacting to a move by the US Senate foreign relations committee on Tuesday giving the green light to a bill that would give Congress the right to review a possible final agreement on the Iranian nuclear issue.

Zarif, Iran's chief nuclear negotiator, said Iran would study the bill "to see if it infringes upon or hinders the capability of the president to carry out the obligations that he is going to assume with Iran."

Israel, which is bitterly opposed to the emerging agreement between Iran and world powers that would rein in but not halt Tehran's nuclear activities, has welcomed the US bill.

Global powers reached a framework agreement for a deal with Iran on April 2. They must now resolve a series of technical issues by a June 30 deadline for a final deal, including the steps for lifting sanctions on Iran, and remaining questions over the possible military dimensions of its nuclear programme.

Iran wants sanctions lifted immediately the deal is signed, while the powers are saying they will be eased gradually, and want a mechanism to ensure they can be swiftly re-imposed if Iran breaks its word.

Zarif also said that Russia's decision to go ahead with the sale of S-300 air defence missile systems to Iran is "fully legal" and has no impact on the talks for a nuclear deal with major powers.

"Russia is fulfilling its contractural treaty obligation to deliver the S-300 defence capabilities to Iran. It had nothing to do with the negotiations," he said during a joint news conference with his Portuguese counterpart Rui Machete.

"I think it is the right decision that Russia has made, it is a contract that we have with Russia which is fully legal and will have no impact on the negotiations."

Tehran talks fail to resolve UN nuclear watchdog questions
Tehran (AFP) April 15, 2015 - The UN atomic agency failed during talks in Tehran Wednesday to resolve long-standing questions over Iran's alleged past efforts to develop nuclear weapons, an Iranian official said.

"We discussed certain solutions to resolve the two outstanding questions, and it was decided to wind up the discussions at the next meeting," said Reza Najafi, Iran's ambassador to the International Atomic Energy Agency, quoted by ISNA news agency.

"We hope to reach this stage at the next session," he said without giving a date, at the end of a one-day visit by chief IAEA inspector Tero Varjoranta and a team of experts.

Iran had agreed to answer agency enquiries about alleged explosive testing and research into nuclear bomb making by last August.

Wednesday's meeting was the first since Iran and six major powers agreed on April 2 the main outlines of potentially historic deal curtailing Iran's nuclear activities in return for sanctions relief.

Western officials say it is crucial for Iran to answer the IAEA's questions about the "possible military dimensions" of its activities before any sanctions can be eased.

Iran rejects the allegations as false information provided the IAEA by the Islamic republic's enemies, complaining that Tehran has not even been given an opportunity to see much of the supposed evidence itself.

Under the April 2 agreement, Iran agreed to scale back dramatically its nuclear programme and submit to ultra-tight IAEA inspections in order to make any eventual dash to make a nuclear bomb extremely difficult and easily detectable.

The accord has a target date of June 30.