BEIJING (AFP) - China's Communist chief Xi Jinping has given the go-ahead for a corruption investigation into the former head of the country's internal security apparatus, the New York Times reported on Monday.

Citing what it described as "sources with elite political ties", the paper said the decision to open the inquiry into Mr Zhou Yongkang was made early this month.

Mr Zhou is a former member of the elite Politburo Standing Committee and one of China's most powerful politicians of the last decade.

It would be the first time for decades that such a high-ranking figure has been targeted in a formal inquiry.

A senior official visited Mr Zhou at his home to inform him of the move and he and his wife have since been under what the paper described as "constant guard", without saying he had been detained.

The New York Times cited five people including "a lawyer with family connections to the party elite" and "the granddaughter of a late leader". All spoke in return for anonymity due to "the risk of recriminations for discussing sensitive politics", the paper said.

"It's not like in the past few months, when he was being secretly investigated and more softly restricted," the paper quoted the lawyer as saying. "Now it's official."

Mr Xi has taken a hard line against graft in the party since coming to power a little over one year ago. He took over as state president in March this year, the culmination of a once-in-a-decade leadership transition.

He has warned that corruption could destroy the party and threatened to stamp down on high-ranking officials, or "tigers", along with low-level "flies".

The ruling party maintains its own internal disciplinary body, which may or may not pass cases to the criminal justice system.

But there is no assurance that the Zhou inquiry's existence would ever be officially confirmed, or its findings announced.

Nonetheless a move against Mr Zhou - who was linked to fallen political star Bo Xilai - would send shockwaves through China's elite.

The reported decision by Mr Xi and other leaders to launch the probe follows a series of inquiries into suspected abuse of power and corruption among officials and oil company executives with ties to Mr Zhou.

China announced in August that four top managers at state-owned China National Petroleum Corp - which Mr Zhou headed from 1996 to 1998 - and its listed arm PetroChina were under investigation for "violation of discipline", a euphemism often used for graft.

Mr Zhou was the party chief of the southwestern province of Sichuan from 1999 to 2002, and in June the official Xinhua news agency reported that its former vice governor Guo Yongxiang had been put under investigation.

Mr Guo also worked in the oil industry for 26 years, according to Chinese media reports.

Last December Xinhua said that Mr Li Chuncheng, who was promoted to mayor of the Sichuan capital Chengdu during Zhou's time in the province, had been removed from his post as the province's deputy party secretary for "serious violations of discipline".

Mr Li was the first high-ranking official to be fired after the Communist power handover.