Ai Weiwei, the Chinese artist and dissident, broke his silence on political topics on Tuesday for the first time since he was released from a prison in China nearly two months ago, describing in Twitter postings the treatment of business colleagues who had been detained with him and expressing support for two other incarcerated dissidents.

Mr. Ai, 54, formerly an outspoken critic of Chinese political and social restrictions, was arrested in April, held for three months by state security officials and later charged with tax evasion arising from his Shanghai art studio business. He was released after Chinese authorities said he had confessed and had been a model prisoner, but he was ordered not to leave Beijing without permission for a year. His tax evasion case is pending.

At the time he was freed, Mr. Ai told reporters in Beijing that he could not talk about his case or anything else and asked to be left in peace. It was not immediately clear why he resumed speaking out now.

In his Twitter post, Mr. Ai said that four business colleagues who were arrested were “illegally detained because of me.” Referring to the four, Liu Zhenggang, Hu Mingfen, Wen Tao and Zhang Jinsong, Mr. Ai wrote, “Innocently they suffered huge mental devastation and physical torture.”

Mr. Ai wrote that Mr. Liu, whom he saw on Tuesday, “had a heart attack when he was at the detention facilities and almost died.” It was unclear from Mr. Ai’s postings whether any of the four colleagues were still in detention.

In a separate Twitter posting, Mr. Ai urged support for Wang Lihong, a rights activist, and Ran Yunfei, a writer and blogger, both of whom are in detention. “If you don’t speak for Wang Lihong, nor for Ran Yunfei, not only you’re the sort that doesn’t speak up for fairness and justice, you have no love for yourself,” he said.

Mr. Ai resumed using his Twitter account on Saturday with a simple “what’s up?” greeting, his first post since April 3, when police officers took him into custody at the international airport in Beijing as he was about to board a flight to Hong Kong.

The arrest of Mr. Ai, whose artworks are exhibited around the world, was broadly criticized as a pretext meant by the authorities to silence him because of his criticism of the Chinese Communist Party. It came as part of a wider repression of Chinese rights activists that began six months ago, during the height of the antigovernment uprisings in the Arab world.

Last month, Mr. Ai said that he had accepted an invitation to become a visiting lecturer at the Berlin University of the Arts next year, but that he did not know whether Chinese authorities would allow him to leave the country to take up the post. Martin Rennert, the president of the university, said at the time that he was confident Mr. Ai would “start working at our university in the near future.”