The top adviser to Iran's Supreme Leader Ayatollah Ali Khamenei said his meeting with Russian President Vladimir Putin on Thursday had been "very constructive and friendly" and that Moscow would invest in the Iranian oil sector.
"Our leader (Khamenei) values improving ties with Russia as strategic partner ... This path will continue ... Russia is prepared to invest in Iran's oil sector," the adviser, Ali Akbar Velayati, told Iranian state television from Moscow.
"Iran and Russia will continue to cooperate in Syria," he added. The two countries support President Bashar al-Assad's forces in the Syrian civil war.
Russia, China and the big European powers say they still back a 2015 multinational nuclear deal with Iran, despite US President Donald Trump's decision to pull out and to re-impose economic sanctions on Tehran that were lifted as part of the accord.
"Putin reiterated that Russia rejects America's decision to impose sanctions on Iran ... He said Russia will stand by Iran and will defend Tehran's rights," Velayati said.
The 2015 nuclear deal lifted most international sanctions on Iran in return for Tehran curbing its nuclear program, under strict surveillance by the UN nuclear watchdog.