The deadline for an agreement over Iran’s nuclear deadline has been unofficially extended by three days to 10 July.

The original deadline was 30 June.

Negotiators on both sides say they are optimistic a deal may be reached by the end of the week.

Several key differences are still to be resolved. These are said to include the nuclear inspections regime, the limits on future nuclear research in Iran, the import of conventional weapons, the timeline of sanctions removal and the conditions under which the sanctions could “snap back” if Iran does not meet targets.

Reports suggest these differences are narrowing daily, as talks continue in Vienna.

The P5+1 group – the US, the UK, France, Germany, China and Russia – are seeking a deal to limit Iran’s nuclear programme to prevent it from developing weapons. In exchange, Tehran would gain relief from international sanctions, normalising its trade relations with the world and benefiting its economy.

Agreeing a deal after 9 July will mean the US Congress, which opposes the negotiations, will have 60 days rather than 30 days to discuss the text of the agreement before they vote on it.

The local press expects this would give Republican critics more time to build opposition to the deal.