TEHRAN (AFP) — Iran warned it would hold the United States responsible if Israel attacks its nuclear facilities, but President Donald Trump’s administration voiced optimism for a peaceful solution Thursday before new talks.

Trump spoke about his diplomacy on Iran with Israeli Prime Minister Benjamin Netanyahu, the White House said, in a telephone call largely focused on an attack in Washington that killed two Israeli embassy employees.

Israel has repeatedly threatened military action against arch-enemy Iran and CNN, citing unnamed US officials, reported Tuesday that Israel was making preparations to strike Iranian nuclear sites despite the ongoing US-Iran talks.

“We believe that in the event of any attack on the nuclear facilities of the Islamic Republic of Iran by the Zionist regime, the US government will also be involved and bear legal responsibility,” Foreign Minister Abbas Araghchi said in a letter to the United Nations.

“Iran strongly warns against any adventurism by the Zionist regime and will respond decisively to any threat or unlawful act by this regime,” Araghchi added.

The nuclear talks, which began on 12 April, are the highest-level contact between the long-time foes since the US in 2018 pulled out of a landmark deal between Iran and world powers, during Trump’s first term in office.

The fifth round of talks, which are mediated by Oman, will take place Friday in Oman and include Steve Witkoff, Trump’s globe-trotting negotiator.

Trump told Netanyahu that the Iran talks are “moving along in the right direction,” White House Press Secretary Karoline Leavitt told reporters.

State Department spokesperson Tammy Bruce said the US would not be holding talks “if we didn’t think that there was potential.”

“I would say that clearly we believe that we are going to succeed,” Bruce said.

But a key sticking point has been enrichment. 

“There are still fundamental differences between us,” Araghchi said on state television, warning “we will not have an agreement at all” if the US wants to prevent Iran from enriching uranium.

The 2015 deal with Iran, which was negotiated by former president Barack Obama, allowed Iran to enrich uranium at low levels solely for civilian energy.