WASHINGTON (REUTERS) - The United States and Iran will reconvene indirect talks aimed at reviving the 2015 Iranian nuclear deal on Thursday (April 15) in Vienna, White House press secretary Jen Psaki said.

There have been doubts about whether the indirect talks, which began last week, might resume this week following an explosion at Iran's key nuclear site on Sunday, which Teheran blamed on Israel, as well as Iran's decision to enrich uranium to 60 per cent, bringing the fissile material closer to bomb-grade.

"We don't have any additional speculation to add to the cause or the origin of the attacks over the weekend," Psaki told reporters.

"The diplomatic conversations, though they will be indirect, will reconvene tomorrow in Vienna. We know this will be a long process but we certainly see that as a positive sign.

"Our understanding is they (the Iranians) plan to attend tomorrow. We are also very open-eyed about how this will be a long process. It is happening through indirect negotiations but we still feel that it is a step forward," she added.

Last week, Iran and its fellow parties to the agreement held what they described as "constructive" talks to revive the deal, which the Trump administration abandoned in 2018, saying its terms favoured Teheran, and re-imposed economic sanctions on Iran.

US Special Envoy for Iran Rob Malley plans to be in Vienna for the talks on Thursday, said a US official who spoke on condition of anonymity.

In the indirect talks, chiefly European diplomats are shuttling between the deal's remaining parties - Iran, Britain, China, France, Germany and Russia - and the United States.

Iran has rejected meeting with US officials.