BEIJING — Three officials believed to be right-hand men of China's former security chief were expelled from the ruling Communist Party on Wednesday over corruption, authorities said. The oustings were the latest sign that Zhou Yongkang, once a member of the Politburo Standing Committee (PSC), China's most powerful body, is being targeted. His fall would send shock waves through China's political establishment. PSC members have generally been regarded as untouchable even after retirement. Ji Wenlin, formerly a vice governor of the southern island of Hainan and before that a secretary to Zhou, was stripped of his party membership, the Central Commission for Discipline and Inspection (CCDI), the party's internal watchdog, said in a statement. Also expelled were Yu Gang, an ex-vice director of the office of the Central Politics and Law Commission (CPLC), and Tan Hong, a former senior staff officer of the Ministry of Public Security, it said in separate statements. Zhou used to head the CPLC, which oversees the public security ministry. Overseas Chinese reports claimed Ji, Yu and Tan were all his secretaries. All three took advantage of their posts and “accepted huge amounts of bribes by seeking gains for others,” the CCDI said, adding that their cases have been transferred to judicial authorities for criminal prosecution. Yu and Ji were also accused of adultery, according to the statements. The news came on the heels of the party's announcement on Monday of the ousting of Xu Caihou, a former vice-chairman of China's Central Military Commission, and another three allies of Zhou's for similar reasons. Xu, who was until 2012 a member of the Communist Party's elite 25-strong Politburo, is the first of its former members to fall in the current crackdown on graft, which follows the ascension of Xi Jinping to power as the head of the party. A number of officials and others with close ties to Zhou have come under investigation in recent months, and the former security chief himself is now at the center of rumors about a corruption probe. Zhou, who amassed huge power before his retirement from the PSC in late 2012, has not been seen in public for months. Analysts say this week's expulsions are a strong signal that authorities are set to make an announcement regarding Zhou. Meanwhile, China's ambassador to the Philippines says economic ties between the two countries are at disappointing levels and both must work to advance their common prosperity. Southeast Asian nations including the Philippines and Vietnam are embroiled in territorial rows with China over the South China Sea, where China claims most of the waterway that is one of the world's busiest shipping lanes. Relations between China and Japan have also been strained by disputed islands in the East China Sea. Ambassador Zhao Jianhua did not refer to the territorial dispute but called the Philippines' share of the Chinese investment pie “too disappointing,” with Philippine companies investing more in China than the other way around. – Agencies