TEL AVIV — Israeli Prime Minister Naftali Bennett held talks with President Vladimir Putin Saturday in the Kremlin over Russia’s invasion of Ukraine, and then spoke with Ukrainian leader Volodymyr Zelensky, an attempt to mediate a conflict that has caused growing civilian casualties and refugees.

Before Mr. Bennett’s visit, diplomacy by President Biden and European leaders failed to stop Mr. Putin from invading Ukraine or rolling back his tanks. In the face of massive Western sanctions, Mr. Putin has found himself increasingly cut off from the world, with few avenues for diplomacy and with his country’s economy unplugged from much of global commerce.

Mr. Bennett’s meeting with Mr. Putin took place "with the blessing of the U.S. administration," said Mr. Bennett’s office, which also noted that it coordinated with Germany and France. After seeing Mr. Putin, Mr. Bennett left Moscow for Berlin, where he met with German Chancellor Olaf Scholz, the prime minister’s office said. Mr. Bennett was joined by Housing Minister Zeev Elkin, who was born in the now Ukrainian city of Kharkiv and assisted with the translation.

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The nearly three-hour conversation with Mr. Putin touched on the safety of Ukraine’s Jewish population and international talks over Iran’s nuclear program, Mr. Bennett’s office said. On Saturday, new demands from Russia—a party to the nuclear talks—threatened to derail efforts to restore the 2015 Iran nuclear deal, a pact that Israel opposes.

Sabbath flight to Moscow

Mr. Bennett flew to Moscow as Russian troops continued to meet fierce resistance from Ukrainian forces, and an agreement to evacuate civilians from two besieged cities fell apart. Russia’s invasion of its smaller neighbor last week has caused civilian casualties and sparked the largest movement of people in Europe since World War II as Ukrainians flee the bloodshed.

Russian President Vladimir Putin, left, Israeli Prime Minister Naftali Bennett, center, and Ukrainian President Volodymyr Zelenskyy.

Russian President Vladimir Putin, left, Israeli Prime Minister Naftali Bennett, center, and Ukrainian President Volodymyr Zelenskyy.

The meeting comes about a week after Mr. Bennett, in a call with Mr. Putin, offered to mediate between Russia and Ukraine. Mr. Putin said during that call that he was "ready for negotiation," a senior Israeli official said.

Throughout the Russia-Ukraine conflict, Israel has found itself caught between powerful opposing forces. Israel’s most important ally, the U.S., and pro-Western Ukraine, with a large Jewish population, have pushed Israel to side strongly with the Ukrainians. At the same time, Mr. Bennett’s government has worried that taking sides would jeopardize its relationship with Russia, which allows Israel the freedom to bomb Iranian positions in Syria.

Russian President Vladimir Putin attends a meeting with Israeli Prime Minister Naftali Bennett in Sochi, Russia, Oct. 22, 2021. 

Russian President Vladimir Putin attends a meeting with Israeli Prime Minister Naftali Bennett in Sochi, Russia, Oct. 22, 2021.  (Sputnik/Evgeny Biyatov/Kremlin via Reuters)

Mr. Bennett has faced pressure domestically to boost support to Ukraine. Israel has so far refused a Ukrainian request for weapons and other military equipment, such as helmets and protective vests, Ukraine’s ambassador, Yevgen Korniychuk, said earlier this week. But Israel has condemned Russia’s invasion and voted for a United Nations resolution demanding an end to the offensive.

Mr. Bennett, an observant Jew, flew to Moscow during the Sabbath, underlining the urgent nature of his mission.

Israel has worked to maintain good relations with the Kremlin and has been keen not to anger Moscow during the conflict. Russia’s launch of a military intervention in Syria in 2015 turned it into an important player in the Middle East. Israel sees Russia’s presence there as a moderating influence among Islamist militant organizations such as Hezbollah and Iran’s increasingly aggressive stance.

Mr. Putin’s stated aim of his invasion and decapitation of the Ukrainian government is denazification of the country, despite Mr. Zelensky’s Jewish origins. Since Russia struck a television tower earlier this week in Kyiv’s Babyn Yar area, the site of one of the worst massacres during the Holocaust, international Jewish condemnation of Russia’s invasion has grown.

Negotiations since December

Mr. Bennett’s efforts follow a series of negotiations and letters exchanged between Washington, Moscow and European capitals since mid-December, when Russia demanded written guarantees that NATO wouldn’t expand eastward and  that NATO withdraw troops and missiles from countries that joined the alliance after 1997.

As Russia built up close to 200,000 troops on the Ukraine border, Germany’s Mr. Scholz and French President Emmanuel Macron were among the leading Europeans to visit Moscow in recent weeks, seeking to persuade Mr. Putin that his security concerns about Ukraine and NATO’s expansion could be dealt with through dialogue.

Mr. Scholz sought to float some form of initiative based around the idea that Ukraine was unlikely to become a NATO member for many years. Mr. Macron suggested some form of neutrality for Ukraine had come up in talks.

Ultimately, the Kremlin didn’t budge on its initial demands and Mr. Putin went ahead with his invasion even while discussions were continuing with the Europeans and days before Russian Foreign Minister Sergei Lavrov was due to meet his French and U.S. counterparts in Europe.

"Yes, there was duplicity. Yes, there was a deliberate choice to launch the war when we were still negotiating peace," Mr. Macron said in late February after a meeting of EU leaders on the Ukraine crisis.

German Chancellor Olaf Scholz, right, stands next to Israeli Prime Minister Naftali Bennett on the terrace of the Federal Chancellery, in Berlin, Germany, Saturday, March 5, 2022. Bennett arrived in Berlin from Moscow after a meeting with Russian President Vladimir Putin at the Kremlin. 

German Chancellor Olaf Scholz, right, stands next to Israeli Prime Minister Naftali Bennett on the terrace of the Federal Chancellery, in Berlin, Germany, Saturday, March 5, 2022. Bennett arrived in Berlin from Moscow after a meeting with Russian President Vladimir Putin at the Kremlin.  (Associated Press)

Both Messrs. Macron and Scholz have spoken to Mr. Putin in recent days, urging him to stop the violence.

For Mr. Bennett the stakes are also high. In addition to Israel’s close relationship with Russia and Ukraine and its efforts not to anger Washington by sitting on the fence over the crisis, Mr. Bennett’s visit comes at a critical moment in the Vienna talks on restoring the nuclear deal.

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Israel has long opposed the 2015 pact and is pressing its partners to ensure that if the deal is restored, pressure is kept on Iran to fully cooperate with international inspectors in Iran and to ensure Iran doesn’t cheat.

Russia has played a leading role in negotiating the restoration of the deal between the U.S. and Iran. However on Saturday, Mr. Lavrov threw a new hurdle in the way of a deal, demanding guarantees from Washington that powerful Western sanctions against Russia over its Ukraine attack won’t disrupt trade between Russia and Iran under a restored agreement.

Write to Thomas Grove at thomas.grove@wsj.com and Laurence Norman at laurence.norman@wsj.com