BEIJING—Chinese authorities said they punished nearly 200 people for spreading online rumors in connection with recent major news events, in a government crackdown on politically sensitive discourse.

The sweep targeted people who the government said spread false Internet rumors regarding events such as the stock-market turmoil and deadly explosions earlier this month in the port city of Tianjin, the Ministry of Public Security said Sunday.

The ministry said the accused expressed remorse for their actions, in which they “misled society and the public, generated and spread fearful sentiment, and even used the opportunity to maliciously concoct rumors to attack [Communist] Party and national leaders.”

Separately on Monday, the official Xinhua News Agency said authorities detained a journalist at a Chinese financial-news magazine for allegedly concocting and spreading false information related to securities and futures trading. Xinhua also said that authorities detained four senior executives at Citic Securities Co. for what they called insider trading, as well as an employee at the securities regulator for alleged insider trading, forgery and receiving bribes.

Wang Xiaolu, a reporter at the Caijing business-news magazine, was detained on Sunday after allegedly confessing to collaborating with other people to fabricate information about securities and futures trading, Xinhua said.