BEIJING (Reuters) - Chinese authorities have widened a crackdown on human rights groups, detaining or questioning more than 50 lawyers and activists in a sweep over the past few days, rights groups say.

Citing the need to buttress national security and stability, President Xi Jinping's administration has tightened government control over almost every aspect of civil society since 2012.

In recent years, the government has detained dozens of Chinese for dissent and Tibetans and Uighurs have complained of rights abuses, prompting criticism from theUnited States.

Amnesty International said on Saturday at least 52 lawyers and activists from Beijing,Shanghai and Guangzhou had been detained or questioned over the previous 48 hours.

Those who have been taken away include the prominent lawyer Wang Yu and several colleagues at the Fengrui Law Firm, which has represented high-profile clients such as Uighur dissident Ilham Tohti and Zhang Miao, a news assistant at German newspaper Die Zeit who was recently detained for over half a year.

The detentions and questionings come on the heels of a months-long campaign in state media to discredit human rights activists for undermining national stability by using social media.

The People's Daily, the Communist Party mouthpiece, said on Saturday that public security authorities had identified Fengrui as a "major criminal organization" that served as a coordinating "platform" involved in dozens of sensitive cases since 2012.

The article highlighted the role of former Fengrui employee Wu Gan, a social media personality known as "Super Vulgar Butcher" who blogs about official misconduct and free speech and has been detained since May. The Fengrui employees are under "criminal detention," the paper said.

Other well-known lawyers taken away in recent days include Li Heping, who represented the blind dissident Chen Guangcheng, and Sui Muqing, a lawyer based in the southern city of Guangzhou.

The Ministry of Public Security did not immediately respond to requests for comment.

"The government is very concerned about activists' growing influence and their ability to use social media to drum up public support," said William Nee, a Hong Kong-basedChina researcher at Amnesty International. "They see the agenda-setting process is getting away from them."

More than 100 Chinese lawyers issued a joint statement on Friday to protest Wang's arrest. Many of them have since been detained, rights groups said.

Last month, a U.S. State Department report on human rights said repression and coercion in China were routine against activists, ethnic minorities and law firms that took on sensitive cases.

(Reporting by Gerry Shih; Editing by Jeremy Laurence)