Iran on Thursday will host a conference on Syria in a bid to take over the role of brokering peace in its beleaguered Arab ally, replacing Kofi Annan who last week resigned as the UN-Arab envoy in the crisis.

But participation in the meeting was looking thin, with no government confirming its foreign minister would be taking part.

Iranian Foreign Minister Ali Akbar Salehi said his country was attempting to revive parts of Annan's plan, notably: implementing a ceasefire, sending humanitarian aid, and laying groundwork for national dialogue in Syria.

"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 in a Washington Post op-ed ahead of the gathering.

But while Salehi was quoted Wednesday in official Iranian media as saying '12 to 13 countries from Asia, Africa and Latin America' would take part in the 'consultative' meeting, he did not identify them.

The conference, due to start at around 7 pm (2.30 pm GMT), is meant to gather foreign ministers, according to the Iranian foreign ministry's announcement of the meet on Monday.

Only those governments with a "realistic position" on Syria were invited, it said, implying countries which shared Tehran's position.

"Military means alone won’t end the crisis, and a political agenda that is neither inclusive nor comprehensive will also fail," Salehi wrote in the Post. "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.

But several foreign ministers invited to the conference sent their regrets.

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

A Lebanese diplomatic official told AFP on Tuesday that his country 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.

And Russian reports relayed in Iran suggested Foreign Minister Sergei Lavrov would also not make it. But they said Russia's ambassador to Tehran would sit in.

Iran's stance on Syria hews to that of Russia, which along with China has blocked three attempts in the UN Security Council to sanction Assad's regime over its big-calibre crackdown on the rebels.

Tehran and Moscow believe Assad's government has been unfairly singled out by Western criticism, and that the rebels' role has been glossed over.

More than 21,000 people have died in Syria since the uprising started in March 2011, according to activists.

Annan, when he announced August 2 he was stepping down as peace envoy, said he believed Assad would go 'sooner or later'.

The former UN chief said "continuous finger-pointing and name-calling" within the Security Council undermined his mission to the point he could not go on.

Tehran squarely put the blame for Annan's lack of success on the United States and its allies. Salehi said last week that 'every time Mr Annan sought to resolve the Syrian crisis, the West created obstacles'.

Iran has given its full support to Assad's regime.

A top aide to Iran's supreme leader Ayatollah Ali Khamenei, Saeed Jalili, said in a meeting with Assad on Tuesday that Iran would not allow the collapse of his regime, calling it part of an anti-Israeli axis in the Middle East led by Tehran.

"Iran will never allow the resistance axis -- of which Syria is an essential pillar -- to break," Jalili said.

Iran accuses Turkey, Saudi Arabia and Qatar of arming the opposition in Syria, in collusion with the United States and Israel, to overthrow Assad.