Tehran, July 3, IRNA � Tehran and world powers were still shy of a breakthrough at nuclear talks on Thursday as foreign ministers flew in to help push for a swift deal and resolve disputes over how sanctions could be lifted and how Iran's compliance would be monitored.

In their first background briefing since talks got underway in Vienna, a senior Iranian official indicated Tehran is 'serious' about working to implement a deal aimed at placing restraints on the country's nuclear program.

'We have moved forward a lot. We are trying our best,' the officials said. 'I'm asked if we will get there. I don't know.'

U.S. Secretary of State John Kerry had said Wednesday that negotiators from the U.S. and five other world powers working to craft a deal with Iran were 'making progress'.

His comments came after negotiators agreed to extend talks to July giving them time to reach a comprehensive solution. This will also keep in place restraints on Iran's nuclear program � and the flow of some money to Tehran � past Tuesday's deadline.

Kerry met with Iranian Foreign Minister Mohammad Javad Zarif on Wednesday for the first time since the extension and both sides indicated that work remains.

�We will continue and we will make progress,' Zarif said. 'We have made progress and we will make progress and we will use every opportunity to make progress.'

The director general of the International Atomic Energy Agency, the UN nuclear agency based in Vienna, headed to Iran to meet with the top leadership and resolve key issues � including a major sticking point in the negotiations, resolving 'possible military dimensions' of the nuclear program Iran has always insisted is for peaceful purposes like energy or medical testing.

Under the terms of the deal now being negotiated by Kerry, Zarif and the other powers, the IAEA has sole responsibility for verifying Iran's compliance. Tehran's answers will be critical to whether the leaders forge forward with a final deal.

Despite recent statements from Ayatollah Ali Khamenei indicating Iran could be backtracking from the 'framework' agreement negotiated in Lausanne in April, a senior U.S official in Vienna said on Monday: 'The agreement will be based on the Lausanne parameters.'

The White House echoed a similar hardline.

Earlier this week, President Barack Obama remained firm on Iran's necessary obligations before a nuclear deal is reached, saying that he is still willing to 'walk away' if Iran does not meet the standards and framework laid out in an agreement.

The president said the goal of the negotiations is not only to rely on trust, which he says can't be gained overnight, but also to 'set up a verifiable mechanism where we are cutting off pathways for Iran to obtain a nuclear weapon.'

Ultimately, Obama said, it is up to the Iranians to decide if they can uphold the terms.

The International Atomic Energy Agency was expected to issue a report Wednesday confirming that Iran has lived up to a key commitment it undertook to reduce its stockpile of nuclear fuel that could be used for weapons.

Iran agreed under the preliminary plan of action signed by both sides in November of 2013 to change a large amount of enriched uranium into a form that can't be used for nuclear arms. Technically, this means Iran has converted the enriched uranium into an oxide form, which is very difficult to be used to build a bomb.

Still, disagreements remain.

Iran still rules out inspection of military secrets, but after a deal if formalized, the country will permit inspections under terms of the Nuclear Non-Proliferation treaty.

'We have red lines, they have red lines,' the senior Iranian officials said Thursday. 'But I can say it is manageable. The ministers are here to bridge the gap in the last days in order to reach an agreement.'

By NBC News