The United States must stand by reformists in the Middle East and North Africa as the euphoria of revolution gives way to the tough work of building democratic societies, former U.S. President George W. Bush said on Tuesday.

Bush, who launched the 2003 invasion of Iraq that deposed Saddam Hussein, called the Arab Spring "the broadest challenge to authoritarian rule since the collapse of Soviet communism."

However, he warned that the difficult path to democracy would test those societies and their supporters.

"There are no guarantees, and there will certainly be setbacks," he said in a speech in Washington. "But if America does not support the advance of democratic institutions and values, who will?"

Bush dismissed the arguments of those who saw inherent risks in democratic change in the Middle East and North Africa and felt the United States should be content "with supporting the flawed leaders they know in the name of stability."

"It is not realistic to presume that so-called stability enhances our national security," he said.

Bush said events in Central Europe after Moscow-backed Communist regimes were overthrown in 1989 showed how initial joy at throwing off dictatorship can give way to disillusionment.

"This is now the challenge in parts of North Africa and the Middle East," he said. "After the euphoria, nations must deal with questions of tremendous complexity."

Bush called on the United States to help reformers build civic institutions and political parties, draw up constitutions, hold elections and establish the rule of law and property rights.

"It takes courage to ignite a freedom revolution," he said. "But it also takes courage to secure a freedom revolution for future generations through structural reform.

"Both types of bravery deserve our strong support."

The 65-year-old Bush, whose public appearances have been rare since he left office in 2009, made the remarks at an event where he accepted the papers of late Czech leader Vaclav Havel for the "Freedom Collection" of documents and artifacts from dissidents at the George W. Bush Institute in Dallas, Texas.