Iran is secretly aiding Syria's repression of anti-government protests by providing anti-riot gear and assistance in blocking protesters' use of internet, US officials have warned.
As part of an attempt its mission to spread its influence across the Middle East, Tehran is also examining ways of helping Shia populations in Bahrain and Yemen rising up against their rulers.
"We believe that Iran is materially assisting the Syrian government in its efforts to suppress their own people," an Obama administration official told the Wall Street Journal.
Assistance has included equipment and technical advice on blocking and monitoring communication between dissidents, and drew on the Iranian authorities' own experience of putting down an uprising that followed the June 2009 disputed election.
A new cabinet was formed in Syria on Thursday after President Bashar Assad of Syria sacked the previous government two weeks ago as a major concession to anti-government protests.
More than 200 people have been killed during the unrest, according to Syria's leading pro-democracy group.
Iran has firm links with Syria, as a bulwark against its arch enemy Israel, while supporting Hezbollah in Lebanon and Hamas in Gaza to the same purpose.
Playing a double-edged game, the Shia theocracy in Tehran is however keen to foment unrest in Arab states such as Bahrain and Yemen that have substantial Shia populations, though those hopes are currently chiefly "aspirational". Help to Bahraini Shias has so far consisted of no more than a "few dozen guns", US officials said.
The White House is however concerned that if unrest in the region continues, that type of assistance could expand and destabilise a major US ally in Bahrain. Washington has called on the Gulf kingdom's Sunni rulers to enact reforms and resist violence.
Telegraph Media Group Limited