Iran is marking the 30th anniversary of the takeover of the U.S. Embassy in Tehran, with anti-American demonstrations. But opposition forces are using the occasion to protest their own government.

An image grab taken from Iran's official Arabic-language Al-Alam TV shows Iranians holding an anti-US rally in Tehran, 04 Nov 2009Thousands of people turned out for a government-sponsored rally outside the old U.S. Embassy in Tehran.

The crowds shouted "God is great" and "death to America" as speakers recalled the events of 1979, when revolutionary students seized the U.S. Embassy and held 52 Americans hostage for more than a year.

The takeover was a victory for the new Islamic Republic, which, earlier in the year, had overthrown the U.S.-backed Shah.

But, 30 years on, a new wave of protesters is challenging the government - in particular, the disputed election of President Mahmoud Ahmadinejad in June.

Demonstrators held counter-protest Wednesday in Tehran - the latest in a series of protests against what opponents say was electoral fraud. Witnesses say police used tear gas to break up the gatherings.

On the eve of the anniversary of the embassy takeover, President Obama said, "We have heard for 30 years what the Iranian government is against; the question, now, is what kind of future is it for."

In a message released Tuesday evening, Mr. Obama says the United States wants to move beyond a past of "sustained suspicion, mistrust and confrontation" and seeks a relationship based upon mutual interests and respect.

The two sides are at odds about Tehran's nuclear program. Earlier this week, Iran's spiritual leader, Ayatollah Ali Khameini, said his country is not interested in talks "pre-determined" by the United States.