A total of 30 officials at the ministerial level or higher have been placed under investigation for corruption or other job-related crimes over the past five years, China's top procurator said Sunday.

Prosecutors have investigated about 13,000 officials at the county level or above for corruption and other job-related crimes since 2008, said Cao Jianming, procurator-general of the Supreme People's Procuratorate (SPP), when delivering a work report of the SPP at the first session of the 12th National People's Congress (NPC).

The work report of China's supreme court also delivered at the session showed that during the same period courts nationwide meted out verdicts on 138,000 cases of bribery and malfeasance involving 143,000 criminals.

The past five years have seen the investigation of several high-level officials including Bo Xilai, a former member of the Political Bureau of the Communist Party of China (CPC) Central Committee, and Liu Zhijun, former railway minister.

Li Dajin, an NPC deputy and Beijing-based lawyer, said China had always attached great importance to anti-graft work. After the 18th CPC National Congress in November, the new leadership raised many new requirements and approaches to anti-graft work, demonstrating its resolve to combat corruption.

Xi Jinping, general secretary of the CPC Central Committee, said at a CPC disciplinary watchdog meeting in January the Party should crack down on "tigers" and "flies" at the same time by dealing with illegal activities of officials on the one hand and tackling malpractices and corruption cases, which closely impact the people, on the other.

Since the 18th CPC national congress, China has remained tough on corruption. Within two months since the congress concluded, the CPC sacked several officials who were suspected of violation of law or discipline, including Li Chuncheng, former vice-secretary of the CPC committee of Sichuan Province.

Meanwhile, spurred on by new leaders' resolve to fight corruption, China's netizens have used the Internet to expose corrupt local cadres.

The recent fall of some officials in the country was caused by online muck-rakers who used China's popular social networking websites to reveal the officials' unlawful behaviors.

During the CPC disciplinary watchdog meeting in January, Xi ordered enhanced restraint and supervision on the use of power and said "power should be restricted by the cage of regulations."

A disciplinary, prevention and guarantee mechanism should be set up to ensure that people in power do not dare to, are not able to and can not easily commit corruption, Xi said.

Li Chaogang, an NPC deputy and Party chief of Beijing's Fengtai District, said "restricting power by the cage of regulations" is the key to anti-corruption campaign.

In combating corruption, it was not enough to rely on self-discipline of people in power and a bigger role should be given to the functions of anti-corruption systems, said Li.

According to the SPP report, prosecutors took about 19,000 bribers to court over the past five years.

At the same time, the SPP set up a national anti-corruption hotline and website, and improved its work in collecting clues and protecting whistleblowers and witnesses, he said.

A national database of bribery cases has been established and more than 2 million searches were conducted, according to Cao.

This year, prosecutors will continue to pay attention to graft cases which harm public interests, Cao said.

The top procurator also warned of outstanding problems in the work of prosecutors.

This year the SPP will work to curb corruption and misconduct among prosecutors and tighten supervision on senior officers of procuratorates, he said.