BEIJING (Reuters) - China investigated more than 25,000 people for corruption in the first six months of 2014, state media said on Friday, amid a nationwide crackdown on graft.

Nearly 85 percent of the cases investigators pursued involved bribes of more than 50,000 yuan ($8,000) or embezzlement of 100,000 yuan, the official Xinhua news agency said, citing the country's top prosecutor, the Supreme People's Procuratorate (SPP).

Such "major cases" were up nearly 14 percent over the corresponding period last year, Xinhua said.

China's leadership under President Xi Jinping has presided over an anti-graft campaign to shore up a ruling mandate shaken by suspicion that officials waste taxpayer money or use their positions for personal advantage.

Xi has said graft threatens the survival of the ruling Communist Party.

China is also going after officials who have fled abroad with illicit funds, Xinhua said. In the first half of the year, 320 suspects in corruption cases were "seized and brought back to China".

"The SPP will set up a leading work group to retrieve bribery funds from overseas, enhance its supervision over major cases, and build a database of information about fugitive officials," the news agency said.

Xi has pledged to go after powerful "tigers" as well as lowly "flies" in the crackdown, which has netted several senior figures, including Xu Caihou, former vice chairman of the Central Military Commission.

Whether the anti-corruption campaign will convince the public that the Party is serious is an open question. China has run such campaigns in the past to little permanent effect, and critics say only real transparency will have a lasting impact.

(Reporting by Michael Martina; Editing by Clarence Fernandez)