Senior diplomats from Iran and major powers have met online on Wednesday to discuss the state of their nuclear deal that is eroding despite conciliatory signals from US president-elect Joe Biden.

The consultations are meant to prepare upcoming talks among foreign ministers from Iran, Britain, France, Germany, Russia and China, according to diplomats.

Iran has far more enriched uranium than allowed under the agreement that was reached in 2015, and has plans to install advanced equipment that could speed up this process, the International Atomic Energy Agency (IAEA) in Vienna said in two recent reports.

The nuclear deal is meant to prevent the Islamic Republic from amassing uranium that could be used for nuclear weapons. In return, major powers promised to end Iran's economic isolation by lifting sanctions.

US President Donald Trump pulled out of the pact and revived US sanctions in 2018. One year later, Iran started abandoning key provisions of the deal. Iran's pragmatic President Hassan Rowhani and his future US counterpart Biden have both said they are willing to return to the agreement.

However, Iranian hard-line parliamentarians pushed through a law earlier in December that would allow the government to ramp up uranium enrichment and block IAEA inspectors.

Wednesday's talks are also overshadowed by the assassination of a high-ranking Iranian nuclear physicist in late November. Foreign Minister Mohammad Javad Zarif has put the blame on Israel, which is opposed to the nuclear deal.

Iran's execution of a dissident journalist on Saturday has further soured the diplomatic atmosphere.