Iran's supreme leader Ayatollah Ali Khamenei on Saturday replaced the head of the elite Revolutionary Guards force, in a surprise move at a time of mounting tension with the West.
State television said General Yahya Rahim Safavi would be stepping down to become a special military adviser to Khamenei and would be replaced by fellow Guards commander Mohammad Ali Jaafari as the new overall head of the force.
The move comes just two weeks after US officials said that US President George W. Bush was set to issue an executive order blacklisting the force as a terror group in order to block its assets.
"Acknowledging General Safavi's 28 years of honest service in different military fields and 10 years of successful leadership of the Revolutionary Guards, I appoint you top adviser in military affairs," said a decree from Khamemei.
A separate decree read: "General Jaafari, taking into account your valuable experience and your brilliant record in the Revolutionary Guards, I appoint you as head of this revolutionary organisation."
No reason was given over the reason for the switch, which had not been anticipated. Khamenei thanked Safavi for his "valuable" service and advised his successor to highlight the "increasing progress" of the Guards. The Guards is a fiercely committed ideological force whose influence has extended beyond the military into politics and the economy.
Safavi explained the Guards' role in an interview last month: "We are a major offensive and defensive power in the Middle East. We have trained and equipped our forces with the latest equipment to defend our soil."
His replacement comes at a time of mounting tension with the West over the Iranian nuclear programme, which Washington argues is aimed at making a nuclear weapon. Tehran insists its atomic programme is peaceful.
Bush has never ruled out military action against Tehran, while French President Nicolas Sarkozy warned last week that Iran risked being bombed if no solution was found to the nuclear crisis.
In recent years, the Guards' influence has also started to permeate all areas of Iranian society, with its engineering arm picking up massive contracts and former cadres moving into crucial political positions.
President Mahmoud Ahmadi-nejad fought for the Revolutionary Guards during the 1980-1988 war with Iraq, and after taking office in 2005 promoted five former Guards members into cabinet posts. But it is business where the Guards now reaps an increasingly substantial income which the United States is seeking to block with the mooted blacklisting of the force.
In 2006, the Guards won a contract worth 2.09 billion dollars to develop phases 15 and 16 of Iran's biggest gas field, South Pars, and a 1.3-billion-dollar deal to build a pipeline towards Pakistan. The Islamic Revolutionary Guards Corps (Sepah-e-Pasdaran-e-Enghlab-e-Islami) was formed shortly after the 1979 Islamic Revolution led by the late Ayatollah Ruhollah Khomeini.
Controlled directly by Khamenei, the force is now believed to number at least 100,000 people. Its ground, naval and aviation branches operate in parallel to the regular armed forces.