China's ruling Communist Party will sustain the pressure in its graft-busting campaign this year and will make corrupt officials in key posts priority targets and aim to investigate all central-level party and government bodies.

The party's internal corruption watchdog, the Central Commission for Discipline Inspection, said the investigations of former security tsar Zhou Yongkang and Ling Jihua, a one-time aid to former President Hu Jintao, had "removed hidden political dangers".

Following a three-day annual planning meeting the commission warned late on Thursday that problems remained.

"Those who hold important posts and are likely to be further promoted but have not stepped back from their serious corrupt behaviors will be 'top priority'," the state news agency Xinhua reported, quoted the commission as saying.

Xinhua said 47 inspection teams had looked into major central party and government agencies, and the commission would aim to cover all of them this year.

The president and party boss, Xi Jinping, has made the fight against corruption, long viewed as a threat to the Communist Party's grip on power, a centerpiece of his leadership over the past three years.

Dozens of senior officials have been jailed and tens of thousands of officials nationwide have been investigated and punished. Zhou Yongkang, once one of China's most powerful politicians, was imprisoned for life last year.

Xi this week said the anti-corruption drive had shown good results and increased public confidence in, and support for, the party.

The long arm of the party's crackdown has even reached abroad. On Thursday, China announced that it had secured the return of a top corruption suspect who had been in Britain, the latest person from a list of 100 overseas fugitives repatriated during the graft crackdown.