Much of the focus on Iran's nuclear program has been on Tehran's enrichment of uranium, but experts also keep a close watch on the Islamic Republic's Arak heavy water reactor.

That's because the facility, some 250 kilometers (155 miles) southwest of Tehran, could produce plutonium, which can be used to make an atomic bomb.

Russia and Ukraine said Thursday they had completed another exchange of captured soldiers, part of an agreement reached earlier in June at peace talks in Istanbul.

"Our people are returning home from Russian captivity," Ukrainian President Volodymyr Zelensky said on social media, as Russia's defence ministry also confirmed the exchange. Neither side said how many soldiers had been freed.

Iran's deputy foreign minister warned the United States on Thursday against intervening in the war to back up its ally Israel, adding that his country was ready to defend itself in case of escalation.

"If the United States wants to actively enter the field in favor of the Zionist regime, Iran will have to use its tools to both teach a lesson to aggressors and defend its national security and national interests," said deputy foreign minister Kazem Gharibabadi, according to state TV.

Israel's defense minister said Thursday that Iran's supreme leader Ayatollah Ali Khamenei "can no longer be allowed to exist" after an Israeli hospital was hit during an Iranian missile attack.

"Khamenei openly declares that he wants Israel destroyed -- he personally gives the order to fire on hospitals. He considers the destruction of the state of Israel to be a goal," Israel Katz told journalists in Holon near Tel Aviv. "Such a man can no longer be allowed to exist."

Russian President Vladimir Putin will visit China later this year for a regional summit, talks with leader Xi Jinping and commemorations marking 80 years since the end of World War II in Asia, the Kremlin said Thursday.

Putin will attend a summit of the Shanghai Cooperation Organization in Tianjin on August 31-September 1, before heading to the WWII events scheduled in Beijing for September 3, Kremlin aide Yuri Ushakov told reporters.

Iran’s foreign minister will meet with European counterparts in Geneva as an Israeli airstrike campaign continues to target his country, state media reported Thursday.

Foreign Minister Abbas Araghchi will travel to Geneva for the meetings Friday, the state-run IRNA news agency report.

U.S. President Donald Trump has told aides he has approved attack plans but is holding off to see if Iran will give up its nuclear program, the Wall Street Journal reported overnight.

He is due to receive an intelligence briefing on Thursday, a U.S. holiday, the White House said, while top U.S. diplomat Marco Rubio will meet his UK counterpart for talks expected to focus on the conflict.

President Donald Trump left the question of whether the United States will join Israeli strikes on Iran up in the air Wednesday, as he said that Tehran had reached out to seek negotiations.

"I may do it, I may not do it. I mean, nobody knows what I'm going to do," Trump told reporters as he supervised the installation of a new flagpole on the White House South Lawn.

As Israel pounds Iran with airstrikes targeting military facilities and its nuclear sites, officials in Tehran have proposed a variety of steps the Islamic Republic could take outside of launching retaliatory missile barrages.

Those proposals mirror those previously floated by Iran in confrontations with either Israel or the United States in the last few decades. They include disrupting maritime shipping through the Strait of Hormuz, potentially leaving the Nuclear Nonproliferation Treaty and attacks by allied militants.

If the U.S. decides to support Israel more directly in its attack on Iran, one option for Washington would be to provide the "bunker-buster" bombs believed necessary to significantly damage the Fordo nuclear fuel enrichment plant, built deeply into a mountain.

Such a bomb would have to be dropped from an American aircraft, which could have wide-ranging ramifications, including jeopardizing any chance of Iran engaging in Trump's desired talks on its nuclear program. Israeli officials have also suggested that there are other options for it to attack Fordo in central Iran as it seeks to destroy the country's nuclear capabilities.