Iran's most powerful authority, Ayatollah Ali Khamenei, said on Thursday the US was using a chemical attack in Syria's civil war as a pretext to interfere in the country and warned it would suffer loss from any intervention.

"In the case of Syria, the chemical attack is a pretext... The Americans try to play with words and pretend that they've become involved in this case for humanitarian aims," Khamenei told a meeting of the Assembly of Experts, a state body.

"I believe the Americans are making mistakes in Syria and they have felt the impact and will certainly suffer loss," he said in the speech, whose text was published on his official website.

Khamenei's words indicate no let-up in Iran's considerable support for Syrian President Bashar al Assad, its closest ally who stands accused by Western powers of launching poison gas into an embattled suburb of Damascus on Aug. 21. Around 1,400 people were killed, according to U.S. officials.

On Wednesday, the head of Iran's elite Quds force, Qassem Soleimani, told the Assembly of Experts that the Islamic Republic would "support Syria to the end", according to the Fars news agency.

But Iran's response to the chemical attack in recent days hints at disagreement within the corridors of power.

In contrast to military commanders, the government of President Hassan Rouhani, a relative moderate, has condemned the use of chemical weapons and warned against military strikes in Syria, but not apportioned blame for the attack.

Assad's government has denied responsibility, blaming what it calls a provocation by Syrian rebel forces aimed at provoking foreign military intervention on their side in the two-and-a-half-year-old conflict. – Reuters