At a news conference with Israeli Prime Minister Yair Lapid following private talks about Iran's rapidly progressing nuclear program, Biden said the U.S. had laid out for the Iranian leadership a path to return to the nuclear deal and was still waiting for a response.
``When that will come, I'm not certain,'' Biden said. ``But we're not going to wait forever.''
Even as he suggested that his patience with Iran was running low, Biden held out hope that Iran can be persuaded to rejoin the agreement. ``I continue to believe that diplomacy is the best way to achieve this outcome,'' he said.
Biden's desire for a diplomatic solution contrasted with Lapid, who said Iran must face a real threat of force in order to give up on its nuclear ambition.
``The Iranian regime must know that if they continue to deceive the world they will pay a heavy price,'' Lapid said at the news conference. ``The only way to stop them is to put a credible military threat on the table.''
Lapid suggested that he and Biden were in agreement, despite his tougher rhetoric toward Iran.
``I don't think there's a light between us,'' he said. ``We cannot allow Iran to become nuclear.''
As he entered office, he was a key priority for Biden to resolve the Iran nuclear deal brokered by Barack Obama's administration and abandoned by Donald Trump in 2018. But administration officials have become increasingly pessimistic about the chances of getting Tehran back into compliance.
Israeli officials have sought to use Biden's first visit to the Middle East as president to underscore that Iran's nuclear program has progressed too far and encourage the Biden administration to scuttle efforts to revive a 2015 agreement with Iran to limit its development.
Israel opposed the original nuclear deal, reached under Obama in 2015 because its limitations on Iran's nuclear enrichment would expire and the agreement didn't address Iran's ballistic missile program or military activities in the region.
Instead of the U.S. re-entering the deal, which Trump withdrew from in 2018, Israel would prefer strict sanctions in hopes of leading to a more sweeping accord.
The U.S. president, who is set to travel to Saudi Arabia on Friday, said he also stressed to Lapid the importance of Israel becoming ``totally integrated'' in the region.
Their one-on-one talks marked the centrepiece of a 48-hour visit by Biden aimed at strengthening already tight relations between the U.S and Israel. The leaders issued a joint declaration emphasizing military cooperation and a commitment to preventing Iran, which Israel considers an enemy, from obtaining a nuclear weapon.
In the joint statement, the United States said it is ready to use ``all elements of its national power'' to prevent Iran from obtaining a nuclear bomb.
Biden, in an interview with Israel's Channel 12 that aired Wednesday, offered strong assurances of his determination to stop Iran from becoming a nuclear power, saying he'd be willing to use force as a ``last resort'' if necessary.
Iran announced last week that it has enriched uranium to 60% purity, a technical step away from weapons-grade quality.
The joint declaration could hold important symbolic importance for Biden's upcoming meeting with Arab leaders in Saudi Arabia as he seeks to strengthen a regionwide alliance against Iran.
``I talked about how important it was . for Israel to be totally integrated in the region,'' Biden said after his one-on-one meeting with Lapid on Thursday.
The president heads to Saudi Arabia after calling the kingdom a ``pariah'' nation as a candidate and releasing a U.S. intelligence finding last year that showed the kingdom's defacto leader, Mohammed bin Salman, like approved the killing of of Jamal Khashoggi, a U.S.-based writer.
Biden declined to commit to mentioning Khashoggi's murder when he meets with the crown prince..
``I always bring up human rights,'' Biden said at the news conference. ``But my position on Khashoggi has been so clear. If anyone doesn't understand it, in Saudi Arabia or anywhere else, then they haven't been around for a while.'' He did not reiterate his position.
Thursday's appearances with the Israeli prime minister could also provide a boost to Lapid, who is serving in an interim capacity until elections in November, Israel's fifth in less than four years. Lapid's main opponent is former Prime Minister Benjamin Netanyahu, and the joint appearance with Biden could help burnish his credentials as a statesman and leader.
Biden and Lapid also participated in a virtual summit with India and the United Arab Emirates, a collection of countries called the I2U2. The United Arab Emirates announced it will help finance a $2 billion project supporting agriculture in India.
Biden didn't mention Israel's upcoming election during the public portion of Thursday's meeting with Lapid, but told reporters ``we had a good beginning of a long, God willing, relationship.''
Biden is expected to meet only briefly with former prime minister Benjamin Netanyahu, with whom he's had a rocky relationship.
Much like Lapid, Biden also faces a political threat from his predecessor. Trump, an ally of Netanyahu who still enjoys strong support from Republican voters despite his attempt to overturn the last election, may run for another term.
Asked in the Channel 12 interview if he expected a rematch, Biden replied, ``I'm not predicting, but I would not be disappointed.''
Given the U.S.'s status as Israel's closest and most important ally, Biden is at the centre of the country's attention during his visit.
He is set to receive Israel's top civilian honour, the presidential medal of honour, from President Isaac Herzog on Thursday.
Biden also planned to meet with U.S. athletes participating in the Maccabiah Games. Also known as the ``Jewish Olympics,'' it's the country's largest sporting event and is held every four years for Israeli and Jewish athletes from all over the world.