Iran’s Foreign Minister Mohammad Javad Zarif has said a long-term nuclear agreement between Tehran and world powers has “never been closer” as the two sides continue negotiations in Vienna.

Foreign ministers of the major powers are expected to return to Vienna on 5 July, in an attempt to reach a comprehensive deal by the extended deadline of 7 July.

“[At] this 11th hour, despite some differences that remain, we have never been closer to a lasting outcome,” Zarif said in a video message released on 3 July from the Viennese hotel hosting the talks.

He added that there is “no guarantee” of success.

US Secretary of State John Kerry agreed that the two sides were “making progress”, but said there was still much work ahead before a deal is reached.

CNN reported that experts from the countries involved have reached a tentative agreement on language dealing with sanctions relief. However, this still had to be presented to the foreign ministers, the US network said, citing a source familiar with the talks.

Iran and the P5+1 group of world powers – the US, the UK, France, Germany, China and Russia – are aiming to reach a deal to give Tehran relief from sanctions in exchange for limiting the development of its nuclear programme.

If a deal is reached, the removal of sanctions is expected to bring significant benefits to the Iranian economy, with the immediate gains including an increase in oil production and exports, and a payout of more than $100bn in frozen overseas oil funds.