THE Iranian state has directly accused the United States of meddling in the deepening crisis over a disputed presidential election and broadened its media clampdown to include blogs and websites.

But protesters took to the streets in growing defiance of the country's Islamic rulers.

The events - including more arrests and a call for another mass opposition march through Tehran - displayed the sharpening attacks by authorities but also the unprecedented challenges directed at the very heart of Iran's Islamic regime: its supreme leader and the cleric-run system.

Any serious shift of the protest anger toward Iran's non-elected theocracy would sharply change the stakes.

Instead of a clash over the June 12 election results, it would become a showdown over the core premise of Iran's system of rule - the almost unlimited authority of the clerics at the top.

For the moment, however, both sides appear to be using the same tactics since the disputed results showed hard-line President Mahmoud Ahmadinejad as the landslide winner.

Opposition leader Mir Hossein Mousavi called for another mass rally in open defiance of Iran's most powerful figure, Supreme Leader Ayatollah Ali Khamenei, who has urged the nation to unite behind the state.

Authorities rounded up perceived dissidents and tried to muzzle websites and other networks used by Mr Mousavi's backers.