WASHINGTON (AFP) — The White House Thursday defended President Barack Obama's stance on Iran's political crisis, amid fresh Republican demands for him to strongly back demonstrators in Tehran.

Obama has warned that US "meddling" in Iran's internal politics would be counterproductive, downplayed policy differences between the two rivals in the disputed poll and vowed to push forward his engagement policy with Iran.

Officials appear concerned that a vehement intervention in the crisis could give Iranian authorities the chance to portray demonstrators as agents of the United States and prompt a crackdown.

But senior Republicans have started to squeeze Obama on the issue, accusing him of treating a regime with long record of antipathy to Washington and opposition demonstrators with moral equivalence.

Obama's vanquished 2008 Republican election foe John McCain has also been hammering the president on his stance on Iran.