Iran on Thursday is hosting an international conference on Syria in the hopes of stopping the bloodshed there and forging a role as peace-broker for its beleaguered Arab ally, officials say.

However signs pointed to the Tehran meeting falling short of its stated goal of bringing together at least a dozen foreign ministers to discuss the crisis.

Instead, some countries -- Kuwait and Lebanon among them -- said they would not show up, while others including Russia and Algeria said they would send lower-ranking diplomats.

"Representatives of more than 20 countries are to attend the consultative conference on Syria," Amir Abdollahian, Iran's deputy foreign minister in charge of Arab affairs, told state television channel IRIB.

He did not identify those countries, or say at what rank they would be represented.

Announcing the gathering on Monday, Abdollahian said the "consultative meeting" would be at foreign minister level and involve "countries having a principled and realistic position on Syria."

Foreign Minister Ali Akbar Salehi said in an op-ed piece published in The Washington Post that his country had three goals on Syria: implementing a ceasefire, sending humanitarian aid and laying groundwork for national dialogue.

"I hereby announce Iran’s readiness to host a meeting of countries committed to immediately implementing these steps in hopes of ending the violence," Salehi wrote.

"Military means alone won’t end the crisis, and a political agenda that is neither inclusive nor comprehensive will also fail," he said. "Iran seeks a solution that is in the interest of everyone."

It would be an "illusion" to think that an orderly power transition could happen "should President Bashar al-Assad abruptly fall," he added.

Salehi was scheduled to give a news conference at 7:30pm (1500GMT) shortly after the meeting opens.

Syria itself would not be represented at the meeting, an official at the foreign ministry in Damascus said.

Russia, which shares Iran's stance in protecting Assad's regime, said its foreign minister, Sergei Lavrov, would not attend.

"Russia has received an invitation to the consultative meeting on Syria," its foreign ministry said in a statement.

"If this meeting actually happens, the Russian side will be represented by Russia's ambassador to Iran."

It added that Moscow supported the goals set out by Iran to resolve the Syrian conflict, which activists say has cost more than 21,000 lives since it erupted in March 2011.

Kuwait has officially told Iran it would not be attending at any level, foreign ministry undersecretary Khaled al-Jarallah told Al-Seyassah newspaper.

A Lebanese diplomatic official also told AFP on Tuesday that Beirut would not be represented because of its policy of "restraint" in the Syrian conflict.

Iran's official IRNA news agency said Algerian Foreign Minister Mourad Medelci would not travel "due to a very busy workload." His deputy foreign minister would go instead.

Iran has steadfastly stood by Assad throughout the conflict.

A top aide to supreme leader Ayatollah Ali Khamenei, Saeed Jalili, flew to Damascus on Tuesday to meet Assad and vow that Tehran will never allow the bond with his regime to break.

But Iran's foreign ministry has in recent days opened the door to including Syria's opposition in a national dialogue.

There was no immediate word from the Syrian opposition and rebels on how they viewed the Tehran conference.

Iran's hasty organisation of the meeting follows the August 2 resignation of Kofi Annan as UN-Arab League peace envoy on the Syria crisis.

The frustrated former UN chief said "continuous finger-pointing and name-calling" within the UN Security Council had undermined his mission.

He also said he believed Assad would go "sooner or later."

Iran, which blamed Annan's departure on US support for Syria's rebels, said it was trying to revive parts of Annan's six-point peace plan.

Tehran's position also hewed closely to that of Moscow, which along with China has blocked three Security Council attempts to sanction Assad's regime.

Russia and Iran believe Western criticism of Assad's heavy-handed crackdown glosses over the role of Syria's rebels in the conflict.

Iran also backs Syria's portrayals of the rebels including foreign fighters as being armed by Sunni rivals Saudi Arabia, Qatar and Turkey.