Russian President Vladimir Putin has sent a letter to Iran's leaders asking them to refrain from military action against Israel while he tries to mediate between the two countries, according to sources familiar with the matter.

The letter was hand-delivered by Russian Defense Minister Sergei Shoigu, who arrived in Tehran yesterday.

Shoigu is scheduled to meet with the Secretary of Iran's Supreme National Security Council, Ali Akbar Ahmadian, and the Chief of General Staff of the Iranian Armed Forces, Mohammad Bagheri.

Shoigu's agenda also includes a meeting with the new Iranian president Masoud Pezeshkian, the Interfax news agency reported.

Iran has threatened to retaliate against Israel for the assassination of Hamas leader Ismail Haniyeh, widely attributed to the Jewish state's intelligence services. Israel has made no official comment on the killing.

Haniyeh, who attended the inauguration of the new Iranian president Pezeshkian. died in an explosion in a secure guest house for foreign dignitaries, in circumstances that remain unexplained for now.

Hours earlier, an Israeli airstrike killed Hezbollah commander Fuad Shukr, a close Iranian ally. Iran's Revolutionary Guard Corps threatened to punish Israel "at an appropriate time, place and manner."

According to the New York Times, Iran's supreme leader, Ayatollah Ali Khamenei, ordered Iran's armed forces to attack Israel in retaliation for Haniyeh's assassination.

There is widespread speculation about possible Iranian actions, as well as a potential Israeli response. On April 13, Iran launched over 300 missiles at Israel. Almost all were shot down by a combination of Israeli and American air defenses.

The possible role of Russia in the conflict between Israel and Iran remains an open question. Reuters reported on August 6 that Putin asked Iran to avoid civilian casualties in any potential military action against Israel.

The same source reported that Shoigu conveyed this message to Tehran. Iran, in turn, has asked Russia to sell it Su-35 fighters, one of Russia's most advanced aircraft. There were no reports of a Russian response to the request, Reuters reported.

The New York Times reported on August 5 that Russia is sending air defense systems to Iran, without specifying which systems. According to Russian sources, Russia is out of weapons because of its operation in Ukraine, and is unlikely to be able to provide its best air defense system to Iran.

Western media also reported that Iran considered Putin's proposal, but demanded high-tech Russian weapons as part of the deal – specifically, Russia's S-400 air defense system, which has a range of up to 400 kilometers and the ability to track multiple targets.

Iran currently possesses the Russian S-300 system since 2016.

Israel currently maintains close communication with Russia, advising Russian forces in Syria of thousands of strikes against "militia" allied to Iran. Russia suspended its air defenses and allowed Israel to operate unhindered.

The war in Ukraine has put Israel in a quandary: it does not want to get on the wrong side of Russia by providing military support to Ukraine.

The US has asked Israel to sell up to eight Patriot missile systems to Ukraine, which is currently under negotiation.

The Patriot missile system is particularly important to Ukraine, as the only available defense against Russian aircraft that launch bombs at a range of about 60 kilometers.

If Putin helps Israel ease tensions with Iran, he will surely ask Israel for some kind of return favor.