This handout picture released by Iran's Atomic Energy Organization on Nov 4, 2019, shows the atomic enrichment facilities at the Natanz nuclear research center, some 300 kilometers south of the capital Tehran. (HO / ATOMIC ENERGY ORGANIZATION OF IRAN / AFP)

BRUSSELS - The European Union (EU) on Monday strongly rejected any attempts to derail diplomatic efforts to revive the Iran nuclear deal currently under way in Vienna, the capital of Austria.

EU foreign affairs spokesman Peter Stano told an online press conference that the reported incident in Natanz "could have been an act of sabotage," but insisted that there had been no official attribution over who was responsible.

The Natanz uranium enrichment site near Tehran was hit by a power outage on Sunday as negotiators in Vienna were seeking to readmit the United States to the 2015 pact aimed at curbing Iran's nuclear ambitions, after former US president Donald Trump withdrew from the deal in 2018.

EU foreign affairs spokesman Peter Stano told an online press conference that the reported incident in Natanz "could have been an act of sabotage," but insisted that there had been no official attribution over who was responsible

"There has been no official attribution and there are several accusations that we are aware of, but it has to be clarified what happened and who is behind it. We still need to clarify the facts in detail as quickly as possible," he said.

ALSO READ: US willing to remove Iran curbs to revive deal

Stano said that any attempt to derail the diplomatic negotiations underway in Vienna to salvage the Joint Comprehensive Plan of Action (JCPOA) must be completely rejected.

"We reject any attempts to undermine, derail or weaken diplomatic efforts on the nuclear agreement. ... All issues concerning the nuclear program have to be resolved by diplomatic means because there is no other sustainable alternative," he stressed.

Two meetings of the JCPOA Joint Commission were held last week in Vienna, chaired by Enrique Mora, the deputy secretary general and political director of the EU External Service Action Service, and attended by representatives from China, France, Germany, Russia, Britain and Iran.

READ MORE: Iran says won't halt nuclear activities until US lifts sanctions

Washington sent a delegation led by US Special Envoy to Iran Robert Malley to Vienna. They did not meet their Iranian counterparts face-to-face, but a shuttle diplomacy approach was adopted with the intensified help of the coordinators.