"I would have wanted to see serious progress by the Chinese government before I make a commitment to attend the opening ceremonies. In the absence of some sense of progress, in the absence of some sense from the Dalai Lama that there was progress, I would not have gone," the senator from Illinois said.

Obama said that Washington failed to exert serious pressure on the Chinese government to arrive at a solution during its talks with Tibetan spiritual guru the Dalai Lama.

"We were not aggressive in encouraging the Chinese government to make serious concessions in its talks with the Dalai Lama," he said at an interactive session in St Louis, Missouri.

Bush said last week that he will attend opening ceremonies for the games in Beijing next month. Some world leaders plan to boycott the event because of China's human rights record and its handling of unrest in Tibet.

Tibetan envoys recently accused China of failing to take any "tangible steps" in last week's talks between the sides. They said that China is agreeing to talks only to reduce international criticism in the matter.