WASHINGTON (AP) -- President Barack Obama on Thursday called for Syrian President Bashar Assad to lead his country to democracy or "get out of the way," his most direct warning to the leader of a nation embroiled in violence. In a wide-ranging speech on the Arab revolt across the Middle East and North Africa, Obama said the United States has a historic opportunity and the responsibility to support the rights of people clamoring for freedoms.

On Syria, Obama said the government "has chosen the path of murder and the mass arrests of its citizens." He praised the Syrian people for their courage in standing up to repression in a bloody crackdown that has killed hundreds.

Obama said the region's revolutions speak to a "longing for freedom" that has built up for years and has led to the overturning of tyrants - with perhaps more to fall. He embraced the call for change and compared it to signature moments of U.S. history such as the American revolution and the civil rights movement.

The president spoke at the State Department in his first comprehensive remarks on the astonishing ripples of change in the Middle East. He hailed the killing of al-Qaida terrorist leader Osama bin Laden and declared that bin Laden's vision of destruction was fading even before U.S. forces shot him dead.

Obama said the "shouts of human dignity are being heard across the region."

The president noted that some "true leaders" had stepped down and that "more may follow." He quoted civilian protesters who have pushed for change in Egypt, Libya, Syria and Yemen but noted that among those countries, only Egypt had seen the departure of a long-ruling autocratic leader.

Obama said that while there will be setbacks that accompany progress with political transitions, the movements present a valuable opportunity for the U.S. to show which side it is on. "We have a chance to show that America values the dignity of the street vendor in Tunisia more than the raw power of a dictator," he said, referring to the fruit vendor who killed himself in despair and sparked a chain of events that unleashed uprisings around the Arab world.