Iran aims to send missiles and drones to Syria and increase the number of its military advisers there to support President Bashar al-Assad in his battle against rebels, a senior Iranian official told Reuters on Friday.

"It is likely that Tehran will need to send military equipment, missiles and drones to Syria ... Tehran has taken all necessary steps to increase number of its military advisers in Syria and deploy forces," the official said on condition of anonymity.

"Now, Tehran is providing intelligence and satellite support to Syria."

For Iran, Assad is a crucial ally, part of its "Axis of Resistance" to Israel and U.S. influence in the Middle East.

Over the past week, anti-Assad rebels have made their swiftest battlefield gains since the civil war began 13 years ago, striking a devastating blow to Assad.

Tehran, alongside Moscow, has long provided military and economic support to Assad. But that has taken a blow after Lebanon's Hezbollah group, the most powerful of Iran's allies in the region and a lynchpin of forces aiding Assad, suffered heavy losses over the past two months in war with Israel.

"Iran and Syria are united in preventing rebels from advancing toward major cities. Syria has not yet requested ground forces from Iran," the senior official said, adding that "for now, the decision is for Syria and Russia to intensify airstrikes."

He said that Tehran had taken all necessary steps to provide military support to Assad's forces.

The foreign ministers of Turkey, Iran, and Russia will meet in Doha on Saturday to discuss the rebel advance in Syria, a Turkish diplomatic source said on Friday. Turkey, a member of NATO, backs the political and armed opposition to Assad's government.

Tehran has asked Turkey "not to align itself with the U.S. and Israel," the Iranian official said, adding that Iran believes Israel and the United States are working together to prevent Iran's allies from regaining strength.

Iranian Foreign Minister Abbas Araqchi will meet his Iraqi and Syrian counterparts on Friday in Iraq's capital Baghdad to discuss the situation in Syria, Iranian state media reported.

"Iran and Iraq are also studying joint defense projects through resistance groups and even regular armies," the Iranian official said.