Standing next to German Chancellor Angela Merkel, Obama said the United States and Germany share "one voice" in condemning the Iranian effort to crush dissent. He said Iran's leaders cannot hide the "outrageous" behavior of clamping down violently on their people.
"We see it and we condemn it," Obama said.
Said Merkel: "We will not forget this."
Obama spoke in a joint White House appearance with Merkel after they conferred privately. The two leaders have met three times since Obama took office, allies linked by such international troubles as the war in Afghanistan and a worldwide recession.
Obama said it was too soon to tell how potential direct contact between the United States and Iran will be affected by the recent events. Attempting to break from his predecessor George W. Bush, Obama has sought to loosen the diplomatic freeze with Iran, but that effort is now in question -- at best.
Keeping pressure on Iran's rulers, Obama emphasized the rights of the people there.
"Their bravery in the face of brutality is a testament to their enduring pursuit of justice," Obama said.
"The violence perpetrated against them is outrageous. In spite of the government's efforts to keep the world from bearing witness to that violence, we see it and we condemn it."
Merkel backed Obama's stand. And she said Iran must be kept from getting a nuclear weapon.
Iran's violent postelection chaos has captured the world's attention and elicited increasingly sharp condemnations from Obama. Iran's ruling clergy have widened the clampdown on the opposition since a bitterly disputed June 12 presidential election, and scattered protests have replaced the initial mass rallies.
At least 17 people have been killed in a state-led crackdown on protesters.
Incumbent President Ahmadinejad was proclaimed the landslide winner over opposition leader Mir Hossein Mousavi.
Obama's comments on Friday got more direct about the two leaders.
He said Mousavi had captured the spirit and imagination of the Iranian people who want a more free society.
And he dismissed statements by Ahmadinejad, who on Thursday compared Obama to Bush. Obama said he is not meddling in Iran's affairs but rather calling for principles recognized around the world.
"A government that treats its own citizens with that kind of ruthlessness and violence and that cannot deal with peaceful protesters who are trying to have their voices heard in an equally peaceful way have moved outside of universal norms -- international norms -- that are important to uphold," Obama said.
State TV in Iran quoted Ahmadinejad as saying on Thursday: "We expect nothing from the British government and other European governments, whose records and backgrounds are known to everybody and who have no dignity. But I wonder why Mr. Obama, who has come with the slogan of change, has fallen into this trap, the same route that Mr. Bush took and experienced its ending."
The Iranian leader has told Obama to "show your repentance."
Obama said he doesn't take such statements seriously.
"He might want to consider looking at the families of those beaten or shot or detained," Obama said. "That's where Mr. Ahmadinejad and others need to answer their questions."
Merkel pledged an effort to identify the victims of violence of Iran -- who they are and what happened to them.
"Iran cannot count on the world turning a blind eye," she said.
Obama used Merkel's visit to promote his working relationship with the German leader, whose support he needs on a range of international matters.
"I trust her when she says something," Obama said.
Both Obama and Merkel promoted efforts in their nations to combat the warming of the planet. Obama's words -- praising Germany's leadership and pushing the United States to show its own -- came as the House moved toward a historic vote Friday on a bill to overhaul U.S. energy policy.
Merkel praised the potential congressional action, saying she would not have expected such a step in the U.S. a year ago, when Bush was president. The bill would impose the nation's first limits on greenhouse gases linked to global warming and shift the country away from some of its reliance on oil, coal and gas.
Obama said the administration and Congress are still working to create "the framework where we can help lead the international effort."
"We're not going to get there all in one fell swoop," he said.
On Iraq, Obama sought to offer perspective as sporadic but deadly bombings continue to unnerve the nation. U.S. combat troops face a June 30 deadline to leave cities there, part of a broader and gradual withdrawal that is to end American involvement under Obama's watch.
The president said bombings will continue, but overall "Iraq's security situation has continued to dramatically improve."
He said the government of Prime Minister Nouri al-Maliki must strengthen the nation's security forces and make progress on the political "give-and-take" leading up to parliamentary elections scheduled for Jan. 30. He said he has not seen as much political progress as he would like.
Obama said Merkel has not committed to taking detainees from the U.S. prison at Guantanamo Bay, but the German chancellor said her country would not shirk its responsibilities and she was confident there would be a satisfactory resolution of the issue.
Obama said he respects Germany's national security concerns, and he said he has been pleased by the general response in Europe to his request that countries help take detainees so the much-criticized prison in Cuba can be shut down.