Turkish sources said a 300-kilogram bomb was found under a mini-bus in Ankara's commercial district on Sept. 10, Middle East Newsline reported. Security agents assumed it was intended for a convoy that included Prime Minister Recep Erdogan.

The sources said the bomb, located several hundred meters from the government complex, was the biggest seen in Turkey in years. They said Erdogan was moved from his office to his home under heavy security.

"We were spared the district a great catastrophe," Ankara Gov. Kemal Onal said on Tuesday.

The sources said Turkish authorities have concluded that the attempted bombing was the work of Al Qaida. They said Al Qaida was probably aided by Turkish operatives.

"There were warnings that Turkey would be the target of a 9/11 attack," a Turkish security source, referring to the Al Qaida suicide air strikes on the United States in 2001, said. "The bomb we found could have killed hundreds of people."

In 2003, 58 people were killed in Al Qaida truck bombings in Istanbul. Last year, Turkey foiled another major Al Qaida bombing plot.