* Fund bound by guidelines on ethical investments
* PetroChina, Leonardo put under observation
* Fund to engage Eni, Saipem in "active ownership" (Adds details from statement)
OSLO, May 5 (Reuters) - Norway's wealth fund is examining Chinese energy firm PetroChina and Italian defense firm Leonardo to see if there is a risk of corruption in future, the central bank said, after former executives at both firms were linked to graft.
Norway's central bank, which has a unit to manage the $935 billion fund, also said in a statement on Friday it would "raise the issue of the risk of severe corruption" with Italian oil and gas group Eni and oil services firm Saipem.
Ethical guidelines drawn up by the Norwegian parliament bar the world's largest sovereign wealth fund from investing in firms that are involved in activities such as producing nuclear weapons or tobacco products, or deemed at risk of corruption.
The fund's Council on Ethics makes recommendations to the central bank's executive board, which decides whether to act.
"The executive board has decided to place the companies PetroChina Co Ltd and Leonardo SpA under observation based on an unacceptable risk that the companies contribute to, or are responsible for, severe corruption," the central bank said.
It said the Council on Ethics had recommended both firms be excluded from the fund's investments but also said both companies "have taken measures against corruption."
"The executive board believes that these measures provide sufficient grounds to observe the development in the future," it said.
At the end of 2016, the fund had a 0.13 percent stake worth $182 million in PetroChina, whose chief executive between 2000 and 2013, Jiang Jiemin, was sentenced in 2015 to 16 years in prison for bribery and abuse of power. Jiang admitted guilt.
The Norwegian fund had a 1.53 percent stake worth $124 million in Leonardo, whose former CEO Giuseppe Orsi was jailed by an Italian court for four-and-a-half years last year for corruption and falsifying invoices. Italy's highest court ordered a retrial in December. Orsi denies the charges.
Leonardo told the Council on Ethics that graft allegations were leveled at the previous management team not the company.
PetroChina and Leonardo did not immediately respond to a Reuters requests for comment on Friday's central bank statement.
The central bank statement also said the executive board had "decided to raise the issue of the risk of severe corruption" with Eni and Saipem, which is controlled by Eni and Italian state lender Cassa Depositi e Prestiti.
The bank described its engagement with both firms as "active ownership," saying this approach was "better suited" to dealing with the issues and reducing risk.
The fund is Eni's third-largest investor with a stake of 1.72 percent and Saipem's fourth-largest investor with a stake of 1.68 percent, according to Thomson Reuters data.
The Council on Ethics said executives and Eni itself were being investigated over allegations of corruption in Nigeria in 2011. Eni has denied that the company or its personnel were involved in any wrongdoing.
Eni declined to comment when contacted by Reuters on Friday.
The Council on Ethics said the Italian prosecutors had accused Saipem of links to corruption, including in Algeria where it was alleged to have paid intermediaries to secure contracts. Saipem has said it could prove the allegations were groundless in court.
Saipem was not immediately available for comment on Friday. (Additional reporting by Stephen Jewkes in Milan; Editing by Edmund Blair)