U.S. Secretary of State Hillary Rodham Clinton delivered a strong warning to Arab world leaders on Thursday -- reform or else.

Wrapping up a four-nation tour of U.S. allies in the Persian Gulf with unusually blunt remarks to a regional development conference in the Qatari capital of Doha, Clinton said economic and political space must be opened up for the Arab world's exploding youth population, women and minorities.

Clinton said the Arab states will face growing unrest, extremism and even rebellion unless they quickly deal with their vanishing oil and water reserves and adopt real economic and political reform.

She also warned that if Arab countries don't improve human rights for women and minorities and improve business climates and end corruption, young people will increasingly turn to radicalism and violence that could threaten the Middle East and the rest of the world.

"In too many places, in too many ways, the region's foundations are sinking into the sand," she told officials at the Forum for the Future conference. "The new and dynamic Middle East. needs firmer ground if it is to take root and grow everywhere."