BEIJING — Ai Weiwei, the Chinese rebel artist, said Thursday that his one-year probation had ended but that the police had told him he could not leave China because of continuing investigations.

Mr. Ai said the probation, which followed his release last June from 81 days of detention overseen by the Beijing police, ended Thursday morning with a handshake between him and an officer at a police station in Beijing. Mr. Ai said that in theory he could now travel outside the capital.

His supporters said Mr. Ai had been detained for political reasons: he is one of the most vocal critics of the Communist Party.

“They told me they had lifted the probation because I had behaved well all year,” he said in a telephone interview as he was dining at a restaurant in Beijing’s Sanlitun neighborhood. “It really surprised me because I violated almost every rule they imposed.”