Concerns are growing in Iran about the health of Supreme Leader Ayatollah Ali Khamenei, who has not been seen in public for three weeks,

The Times of London on Thursday quoted Iranian sources as saying that Khamenei collapsed recently during a private meeting and since then has been convalescing or receiving treatment. His last public appearance was in Tehran on October 5.

Related stories:

Reports suggest that he has had a relapse of a chronic illness. Khamenei became supreme leader in 1989 and has no appointed heir. His death, or even a prolonged absence, could prompt a power struggle as negotiations with the West over Iran’s nuclear program reach a critical stage, the British newspaper reported.

According to the report, loyalists grew concerned when he did not send his customary goodwill message to Iranians departing for the haj, the pilgrimage to Mecca, two weeks ago. He also failed last week to give his annual address marking the festival of Eid al-Ghadir, the most important date in the Shia Muslim calendar.

“It seems the illness is worse than we thought. People are scared that this could be the end,” one supporter was quoted as saying by The Times.

Hossein Rostami, a Khamenei loyalist who runs the hard-line website Amariyoun, wrote on Facebook: “It is not good news coming our way from our master ... Pray deeply for him.”

According to The Times, Khamenei’s supporters fear that he might be succeeded by Akbar Hashemi Rafsanjani, the former president. Such a development would be a disaster for conservatives, who loathe Rafsanjani’s ties with reformist groups.

After being blocked by Ayatollah Khamenei from running again for president in June’s election, Rafsanjani threw his weight behind Hassan Rohani , who won by a landslide.

Khamenei, The Times reported, has overseen the rapid expansion of the nuclear program. He has backed President Rohani’s more moderate approach, but hardliners depend on him to block any deal with the West that cedes too much ground.

If the supreme leader dies and is replaced by Rafsanjani, hardliners fear a reformist coalition with Rohani that could undermine the power base of the conservative establishment.

“Rafsanjani has been scheming for 30 years to turn Iran into Saudi Arabia — a dictatorship backed by the West,” a Khamenei loyalist said.

Rumors about Khamenei's failing health have circled in Tehran for years, however. “I’ve learned not to get too excited about claims that Khamenei is about to die,” a Western intelligence official in the Gulf was quoted by The Times as saying.

Reports by state-owned news outlets in Syria this week said Khamenei met in Tehran with a delegation of Syrian Muslim clerics. During the meeting, the reports said, the supreme leader stressed Iran's support for Syria, which he said was on the brink of a "dark war."

Khamenei also reportedly said: "The Syrian nation and the Syrian government will defeat the enemies of Islam, the enemies of humanity and the enemies of the region."

Follow Ynetnews on Facebook and Twitter

