Obama: Mideast Political Transitions Will Take Years

President Barack Obama on Thursday invoked the killing of Osama bin Laden as a chance to recast relations with the Arab world and said the top U.S. priority was to promote democratic change across the region.

Obama, in his much-anticipated "Arab spring" speech, also ratcheted up pressure on Syrian leader Bashar al-Assad, saying for the first time that he must stop a crackdown on protests and lead a democratic transition "or get out of the way."

He hailed popular unrest sweeping the Middle East as a "historic opportunity" and said the U.S. future was bound to that of the region now caught up in unprecedented upheaval.

"The people have risen up to demand their basic human rights. Two leaders have stepped aside. More may follow," Obama told an audience of U.S. and foreign diplomats at the State Department in Washington.

His bid to reset ties with the Arab world also faced skepticism over what many have perceived as a hesitant and uneven response to the region's uprisings that threaten both U.S. friends and foes.

Struggling to regain the initiative in a week of intense Middle East diplomacy, Obama was seizing an opportunity to reach out to the Arab world in the wake of the death of Osama bin Laden at the hands of U.S. Navy SEAL commandos.

"We have dealt al Qaeda a huge blow by killing its leader," Obama said. "Bin Laden was not a martyr, he was a mass murderer ... Bin Laden and his murderous vision won some adherents but even before his death al Qaeda was losing its struggle for relevance."

Seeking to back democratic reform with economic incentives, Obama planned to announced billions of dollars in aid for Egypt and Tunisia to bolster their political transitions after revolts toppled autocratic leaders.

Obama's speech was his first major attempt to put the anti-government protests that have swept the Middle East in the context of U.S. national interests.

He has scrambled to keep pace with still-unfolding events that have ousted long-time leaders in Egypt and Tunisia, threatened those in Yemen and Bahrain and engulfed Libya in civil war where the United States and other powers unleashed a bombing campaign.