A top adviser to Iran's Supreme Leader Ayatollah Ali Khamenei said he had a "very constructive and friendly" meeting with Russian President Vladimir Putin in Moscow.
An Iranian delegation led by Ali Akbar Velayati met Putin in the Russian capital on July 12, the Kremlin said.
Velayati told Iranian state television from Moscow that Khamenei "values improving ties with Russia as a strategic partner" and that Moscow was "prepared to invest in Iran's oil sector."
Putin's spokesman, Dmitry Peskov, said that Velayati handed Putin letters from Khamenei and Iranian President Hassan Rohani, but refused to elaborate.
Russia’s Interfax news agency reported that the meeting also involved Russian Foreign Minister Sergei Lavrov, while the Iranian delegation included the head of Khamenei's board of advisers Ali Asghar Fathi Sarbangoli and Iran's ambassador to Russia, Mehdi Sanai.
Velayati also said Iran and Russia would "continue to cooperate in Syria," where both countries support President Bashar al-Assad's forces in the seven-year civil war there.
The meeting came as Iran braces for renewed U.S. economic sanctions after Washington pulled out of the Iran nuclear deal signed in 2015 between Tehran and world powers.
Facing revived sanctions from the United States and the possible knock-on collapse of its business dealings with Europe, Iran is looking to Russia and China for investment and to purchase its oil.
On July 11, Putin held talks at the Kremlin with Israeli Prime Minister Benjamin Netanyahu, who told the Russian leader that "Iran needs to leave Syria."
The United States and Israel want Iran to pull out from Syria, but Russia has warned it would be unrealistic to expect Iran to fully withdraw from the country.
The Iranian presence in Syria is expected to be on the agenda of a July 16 meeting in Helsinki between Putin and U.S. President Donald Trump.