Tehran, Iran (CNN) -- As marchers gathered on the streets of Tehran on Wednesday, the 30th anniversary of the U.S. Embassy takeover, U.S. President Barack Obama nudged Iran on making choices for its future.
"Iran must choose," Obama said in a statement late Tuesday. "We have heard for thirty years what the Iranian government is against; the question, now, is what kind of future it is for. It is time for the Iranian government to decide whether it wants to focus on the past, or whether it will make the choices that will open the door to greater opportunity, prosperity, and justice for its people."
Obama's remarks came as the streets of the Iranian capital grew tense once again, as they have on numerous occasions since reformists began demonstrating after disputed presidential elections in June.
November 4 is an official holiday in Iran and anti-American rallies were expected to mark the events of 1979 when Islamic students stormed the U.S. embassy and held 52 Americans hostage for 444 days.
But anti-government protesters were also expected to take to the streets. At least 2,000 opposition supporters were already out in Tehran's 7 Tir Square, a witness told CNN. Police and members of the pro-government Basij militia were out in force Wednesday and were clashing with counter-demonstrators, who had been issued stern warnings by authorities not to march.
Obama noted how the embassy takeover reshaped U.S.-Iranian relations.
"This event helped set the United States and Iran on a path of sustained suspicion, mistrust, and confrontation," he said. "I have made it clear that the United States of America wants to move beyond this past, and seeks a relationship with the Islamic Republic of Iran based upon mutual interests and mutual respect."
Obama said America has demonstrated willingness to work with Iran over nuclear issues by recognizing its right to peaceful nuclear power and accepting a recent proposal by the watchdog International Atomic Energy Agency.
"We have made clear that if Iran lives up to the obligations that every nation has, it will have a path to a more prosperous and productive relationship with the international community,' Obama said.
He said the world continues to bear witness to the Iranian people's "calls for justice and their courageous pursuit of universal rights."
The Iranian government has arrested more than 1,000 people in a massive crackdown after the June 12 election, in which the incumbent, President Mahmoud Ahmadinejad, was declared the overwhelming winner.
The government accused several reformists, including opposition candidates Mir Houssein Moussavi and Mehdi Karrubi, of spreading anti-government propaganda and fueling the anger among the public.
But despite warnings from hardline leaders, Iran's reformists have largely refused to back down. They released the names of 72 protesters they say were killed in the unrest that followed the election -- more than double the government's official number.
And they have chosen important anniversaries, like Wednesday's, to march defiantly on the streets.
CNN's Reza Sayah and journalist Shirzad Bozorgmehr contributed to this report.