HONG KONG — A spokesman for China’s Foreign Ministry on Friday criticized a decision by The New York Times to publish a lengthy investigation into assets accumulated by the family of Prime Minister Wen Jiabao, saying that the article “smears China and has ulterior motives.”

Speaking at a regularly scheduled daily briefing in Beijing, the spokesman, Hong Lei, also said that the Chinese government’s decision to immediately block access to the English- and Chinese-language Web sites of The Times on Friday morning was taken “in accordance with laws and rules.”

China’s censors also moved with unusual swiftness on Friday to delete any social media postings alluding even tangentially to the article, which cited publicly available corporate documents in reporting that Mr. Wen’s family has controlled assets worth at least $2.7 billion.

Sina Weibo, a very popular microblogging service similar to Twitter and traded on the Nasdaq in New York, on Friday morning immediately deleted the unofficial account that had been used to promote the culture and arts coverage on the Chinese-language site of The Times and that had nearly 60,000 followers. The site’s official account had been blocked since the site began operations in late June.