Negotiators have extended talks on Iran's nuclear programme for a comprehensive agreement until July 2015 after failing to meet a Monday deadline, diplomats said.
But Iran's President Hassan Rouhani said on Monday that a nuclear deal with the six world powers would be done despite a missed deadline in Vienna that prompted a seven-month extension in talks.
"This path of negotiation will reach a final agreement. Most of the gaps have been removed," he said on state television.
His comments were similar to those of US Secretary of State John Kerry who insisted "real and substantial progress" was made during the talks. He called on US politicians not to impose new sanctions on Tehran.
"We have made real and substantial progress," Kerry said in Vienna. "This is not the time to get up and get away.... We look for your support (in Congress) for this extension."
Iran and six powers - the US, China, Russia, Britain, France plus Germany (P5 1) - have been negotiating for six days in the Austrian capital to turn an interim accord reached with the Islamic Republic a year ago into a lasting agreement.
The six nations want Tehran to scale back its nuclear programme in exchange for a lifting of sanctions.
Negotiators agreed to nail down by March 1 what needs to be done by Iran and the six nations it is negotiating with, and by when. A final agreement is meant to follow four months later.
Kerry praised his Iranian counterpart Mohammad Javad Zarif, saying he had "worked deligently and approached these negotiations in good faith and with seriousness of purpose".
"That's what it takes to try to resolve the kind of difficult issues here," Kerry said.
Plea to negotiators
Kerry also urged negotiators to "keep what is discussed in these negotiations exclusively among the negotiators".
"If the facts are out there being bandied back and forth in the public domain ... they often can end up defeating good ideas before they get off the ground," he said.
Al Jazeera's Jonah Hull, reporting from Vienna, said one of the sticking points was uranium enrichment by the Iranian government.
Our correspondent said that despite talking about "gaps" that made it difficult to meet the Monday deadline, negotiators were not willing to talk about those gaps in detail.
The International Atomic Energy Agency said on Monday Iran had taken the necessary steps to continue to comply with an interim nuclear agreement, the Reuters news agency reported.
Some progress has been made but we need to discuss some issues with our capitals. We will meet again before the new year.
Trita Parsi, president of the Washington-based National Iranian American Council, told Al Jazeera it was imperative for all parties to continue negotiations.
"It's important that they're continuing negotiations to reach an agreement, but there is big disappointment at missing the deadline, and the environment will be more doubtful, unforgiving in both Washington and Tehran," he said from Vienna.
After 12 years of rising tensions, negotiators sought to reach a deal by Monday midnight aimed at easing fears that Tehran will develop nuclear weapons under the guise of developing civilian energy - an ambition Iran denies.
Iranian officials have refused to reduce the volume of uranium they are capable of enriching, a stand western officials say is unacceptable as this would potentially allow the country to amass enough fissile material for an atomic bomb in a short time.
A second sticking point is the pace and sequencing of sanctions relief. Iran wants them terminated swiftly, not suspended and gradually scrapped, depending on the degree of Iranian compliance with the deal terms, as the West wants.
Another dispute is over the deal's duration: Western countries want it to be up to 20 years but Iran wants it much shorter.
Benjamin Netanyahu, Israel's prime minister, welcomed the apparent lack of progress at the Vienna talks.
"No deal is better than a bad deal. The deal that Iran was pushing for was terrible. A deal would have left Iran with the
ability to enrich uranium for an atom bomb while removing the sanctions," Netanyahu said.
"The right deal that is needed is to dismantle Iran's capacity to make atomic bombs and only then dismantle the sanctions.
"Since that's not in the offing, this result is better, a lot better," he said, in response to news the Vienna
talks were likely to break off and resume next year.
Source: Al Jazeera and agencies