The ruling Chinese Communist Party's disciplinary arm said on Friday it is investigating a vice minister in the country's powerful intelligence agency.
In a tersely worded statement on its official website, the party's Central Commission for Discipline Inspection (CCDI) said it is investigating Ma Jian, vice minister for national security.
"Ma Jian is suspected of serious violations of discipline and the law," the statement said, using a formulation which normally refers to corruption.
Ma is the most senior official in China's powerful state security apparatus to be investigated since Beijing ended months of speculation by announcing a probe into former security czar Zhou Yongkang last July.
China's national security ministry is a powerful organization analogous to the KGB under the former Soviet Union, which has no official website and no public spokesperson or press office.
According to Reuters, several officials under Ma's control are also "assisting with the investigation," the agency quoted an unnamed source as saying.
Ma was director of the ministry's "No.8 bureau", which is responsible for counter-espionage activities against foreigners, mainly diplomats, businessmen and reporters," Reuters said, adding that his position has now been taken over by fellow vice-minister Qiu Jin.
According to Hong Kong's English-language South China Morning Post newspaper, Ma has close links to Ling Jihua, an aide to former president Hu Jintao who was put under investigation for graft last month.
The paper had earlier reported that several of Ma's close relatives were also part of the investigation, which is believed also to be linked to activities at the high-tech Founder Group, owned by prestigious Beijing University.
Founder chief executive Li You is suspected of financing massive securities trades carried out by one of Ma's relatives, and was taken away for questioning last week, the paper said.
Since taking power in November 2012, President Xi Jinping has launched an unprecedented corruption campaign, pledging to take down both high-ranking "tigers" and low-ranking "flies."
Former state prosecutor-turned-whistleblower Shen Liangqing, who wrote a book analyzing the CCDI's methods, said the investigation of Ma is intimately bound up with factional politics at the heart of the party.
"The anti-corruption campaign is just an excuse," Shen told RFA on Friday. "The Chinese Communist Party leadership's anti-corruption campaign is actually highly selective.
"It's a question of might is right, and whoever is in power says that other people are corrupt. It's a mere tool for the power struggle."
Ling Jihua's status as a political ally of former president Hu Jintao is the crucial factor in Ma's case, Shen said.
"Against the backdrop of a political power struggle, [Xi] targets Ling Jihua, who was a member of Hu Jintao's Youth League faction," he said, referring to the former president's power base in the Communist Party Youth League.
"Going after Ling Jihua is a slap in the face for Hu Jintao, and a very hard one at that," Shen said.
Chongqing-based political commentator Zhang Qi likened Xi's campaign to the jettisoning of selected individuals aboard a ship carrying a precious cargo, to prevent it taking everyone down with it.
"Nobody wants to be thrown overboard, so they all wait to sink together," Zhang said. "Since he came to power, Xi Jinping has used this campaign as a way to save the party, and to protect party rule.
"The sort of actions they are taking could address the problem of public anger over corruption in the short-term, and boost the leadership's prestige.
"But we have to ask ourselves whether this consolidation of their power will lead to imperialism or towards peaceful evolution.
"How is Xi Jinping going to solve the systemic social problems of people's welfare once the anti-corruption movement is over?"
Reported by Qiao Long for RFA's Mandarin Service. Translated and written in English by Luisetta Mudie.