The president of Iran, Mahmoud Ahmadinejad, has come under harsh and unprecedented criticism from his usually close supporters, the Revolutionary Guards, in a move that suggests rifts among the Islamic Republic's power centres are widening.
An article in the most recent issue of the Guards' monthly magazine took the polarising president to task for declaring recently that, after the supreme leader, it is his government and not parliament that is the country's highest authority.
"Does being on top justify whatever action the government thinks right, disregarding the law?" asked the magazine, Payam-e Enghelab (Message of the Revolution), in a story entitled: "Is parliament at the centre of affairs or not?"
Conservative parliamentarians, judiciary officials and some clerics previously have accused Mr Ahmadinejad of trying to amass power in the office of the presidency at the expense of parliament. But this was the first time the Revolutionary Guards have spoken against him publicly.
The elite military force has grown in power and influence since Mr Ahmadinejad - a former Revolutionary Guard - came to office in 2005, and is usually considered his staunch supporter.
The Guards played a key role in quelling last year's unrest that was ignited by Mr Ahmadinejad's disputed re-election. But some of the force's leaders are said to be unhappy that he has not rewarded them with more of a say in decision-making.
Analysts suspect the magazine was encouraged to publish the article by the office of Iran's supreme leader, Ayatollah Ali Khamenei. If so, however, this does not mean there is a major rift between the ayatollah and the president: it is more likely to be a warning shot aimed at reining in Mr Ahmadinejad, analysts said.
"It [the article] should not be turned into a narrative of withdrawal of support for Ahmadinejad and a sign of his imminent downfall," said Farideh Farhi, an Iran expert at the University of Hawaii. "But it should give pause to those who keep explaining Ahmadinejad's success in maintaining power in terms of his base of support in the Guards."
Ayatollah Khamenei has been supportive of the president, even declaring at the time that Mr Ahmadinejad's disputed June 2009 election victory a "divine" blessing. To abandon the president now would mean a huge loss of prestige for the supreme leader. During his recent landmark visit to Qom, Iran's clerical nerve centre, the ayatollah again praised Mr Ahmadinejad's government.
But the supreme leader is also close to some of the president's key conservative rivals, such as the influential parliamentary speaker, Ali Larijani. They, like Mr Ahmadinejad, have allies and influence within the Guards. In September, Ayatollah Khamenei publicly called on Mr Ahmadinejad to accept more criticism and improve co-operation with parliament.
"It looks like someone from Larijani's camp may have been speaking to the supreme leader's office, saying 'we really have to get things working between the executive and parliament',"said Scott Lucas, an Iran expert at Birmingham University in England.
A senior analyst in Tehran, who declined to be identified because of the sensitivity of the subject, agreed, saying: "The usual behind-the-scenes lobbying and occasional grumbling by Larijani and others have failed, leading to the need to give Ahmadinejad a more pronounced public warning."
Ayatollah Khamenei has frequently called for national unity. The continuing and transparent divisions within Iran's power structure come as Tehran is trying to cope with sanctions over its nuclear programme and readying itself for the possible resumption of nuclear talks with world powers later this month.
At home, the regime is braced for the impact of Mr Ahmadinejad's cornerstone economic plan: slashing billions of dollars of subsidies for essentials such as food and fuel.
The Guards magazine also criticised Mr Ahmadinejad's office for promoting an "Iranian school of thought" rather than an Islamic one.
This was directed at the president's controversial chief of staff, Esfandiar Mashaei, who has spoken of an "Iranian" school of Islam. This angered conservative clerics, who said it smacked of secular nationalism and have called for Mr Mashaie's resignation.
But Mr Ahmadinejad has stood by him and there is speculation that he is grooming his chief of staff to run in the 2013 presidential elections. The Guards' article was another reminder that any such move will face vociferous opposition.
The magazine called on Mr Ahmadinejad to focus on "real" issues such as unemployment and inflation, instead of marginal or divisive ones. But the publication's strongest words were about Mr Ahmadinejad's claim that the executive, not parliament, is the most important branch of government. The president suggested in September that an edict by Ayatollah Khomenei, the late leader of the Islamic Revolution, giving parliament primacy was outdated because it was issued before Iran abolished the post of prime minister.
Mr Larijani has responded by saying that Ayatollah Khomenei saw parliament as a defence against dictators, such as the American-backed Shah he ousted in 1979.
The Guards' magazine said: "The superficial interpretation of Imam Khomeini's remarks and changing them in a way that meets a few people's interests for a short time is an irreparable mistake."
Despite the intensifying criticism of Mr Ahmadinejad from fellow conservatives, his position is seemingly safe because he retains public, if sometimes qualified, support from Iran's supreme leader, analysts said.
"Khamenei will continue to back him unless the president's domestic policies and performance completely fail and become a serious threat to the system and thus to the Supreme Leader," the analyst in Tehran said. "But there is no sign of Khamenei dissociating himself from the president yet."