BEIJING—China blocked access to several foreign media outlets, intensified a crackdown on political activists, and fired a fresh salvo of criticism at the U.S. on the eve of a ceremony Friday marking the award of the Nobel Peace Prize to Liu Xiaobo, a jailed Chinese dissident.

A hastily established Chinese organization also held a rival ceremony Thursday to present the inaugural "Confucius Peace Prize" to a Taiwanese politician—even though he was not present and his office said he had no plan to accept the award.

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