U.S. Secretary of State Hillary Clinton leaves Washington for Turkey on Thursday, beginning a 12-day global diplomatic tour.

In Istandbul, she'll meet with leaders supporting the NATO effort to oust Libyan dictator Moammar Ghadafi.

On Wednesday, Clinton said she believed that Gadhafi's days in power "are numbered."

She also said Gadhafi associates were sending mixed messages about whether he would be willing to step down.

"We are still getting contradictory signals from Col. Gadhafi's camp," she told reporters at a joint news conference with visiting Russian Foreign Minister Sergey Lavrov. "He has yet to meet the red lines that are set by the international community to cease violence against his people, withdraw his forces and step down from power."

"So although neither of us can predict to you the exact day or hour that Gadhafi will leave power, we do understand and agree that his days are numbered," Clinton said.

Her visit to Turkey comes just one day after police in the Islamic country arrested 15 suspected al Qaeda militants.

Authorities believe they were planning an attack on the U.S. Embassy in Ankara.

Reports say the suspects had more than 1,500 pounds of bomb-making chemicals.

Clinton will meet Saturday with Turkish officials for talks that are expected to concentrate on Middle East peace efforts.

On Sunday, she travels to Greece for talks that are likely to be dominated by that country's financial crisis and Greek relations with Turkey.