Qasem Soleimani, commander of the Iranian Revolutionary Guards' elite Quds Force, has visited Moscow for the second time, Lebanese newspaper As-Safir reported on Tuesday.
According to the newspaper, the alleged meeting occurred last week.
The newspaper did not specify whom Soleimani met in Moscow. Soleimani is believed to coordinate the Iranian campaign against ISIS and other groups in Iraq and Syria. He is subject to a UN travel ban.
The Lebanese publication speculated that the visit involved Russian-Iranian efforts to coordinate actions in Syria.
This report follows a senior Israeli security source's claim that Soleimani recently sent hundreds of Iranian soldiers to fight rebels in Syria. According to this source, Iranian forces are fighting alongside Hezbollah for the city of Zabadani in southwest Syria, not far from the Lebanese border.
The only Iranian forces known to be active in Syria until now were the Basij, a paramilitary group. Regarding reinforcement of Iranian troops, the Israeli source said that "this is being done in light of Assad's desperation and with Iranian-Russian coordination, following Soleimani's meeting with Russian President Vladimir Putin."
Following Soleimani's alleged earlier visit to Moscow, a Iranian source reported that the commander had arrived in Russia to discuss transfer of advanced S-300 missiles to the Islamic Republic.
Russia and Iran have a shared interest in supporting Syrian President Bashar Assad as much as possible. The New York Times reported last week that Russia has been building a secret base in Syria and sent a delegation of military advisers. It was further reported that Russia had brought temporary housing units to the port city of Lattakiya, capable of housing up to 1,000 advisers and other military personnel.
The report claimed that while there was no indication that Russia intends to deploy significant ground forces in Syria, the base could be used to transfer military equipment or as a launching pad for airstrikes.
Russia is one of Syria's only international allies, along with Iran and Hezbollah.
A few days after the New York Times report, the Russian Foreign Ministry confirmed for the first time that Russian military experts were in Russia.
Also Tuesday, Russian President Vladimir Putin strongly defended Moscow's military assistance to the Syrian government, saying it's impossible to defeat the Islamic State group without cooperating with Damascus.
Speaking at a meeting of heads of states at a Moscow-dominated security alliance of ex-Soviet nations in Tajikistan, Putin urged other nations to follow Russia's example and offer military support to Assad's government.
"We are supporting the government of Syria in the fight against a terrorist aggression, are offering and will continue to offer it necessary military-technical assistance," Putin said in televised remarks. "Without an active participation of the Syrian authorities and the military, it would be impossible to expel the terrorists from that country and the region as a whole, and to protect the multi-ethnic and multi-confessional Syrian people from destruction."
He said that Assad was ready to conduct political transformations and engage a "'healthy part of the opposition," but added that "pooling forces in the fight against terror takes the priority now."
Putin shrugged off allegations that Moscow's support for Assad has sparked a flow of refugees, saying that without Russia's support for Assad's regime the number of Syrian refugees heading to Europe would have been even bigger.
"People are fleeing Syria primarily to escape fighting that has been fueled from the outside with supplies of weapons and hardware, they are fleeing to escape terrorist atrocities," he said. "Without Russia's support for Syria, the situation in the country would have been worse than in Libya, and the flow of refugees would have been even bigger."
The Russian leader is set to address the Syrian crisis when he speaks to the UN General Assembly later this month, and observers in Moscow believe he wants a Russian military force on the ground to be ready by that time.
The Associated Press contributed to this report.