Petroleo Brasileiro SA's next CEO is already working within the Brazilian state-controlled oil firm and is talking with employees about business plans, four sources told Reuters.

Roberto Castello Branco, named by president-elect Jair Bolsonaro's economic team to take the helm at Petrobras, is expected to take up the chief executive role next year pending approval by the company's board.

However, the sources, who spoke on condition of anonymity, said Castello Branco already had access to internal documents and had taken part in discussions around Petrobras' new five-year strategic plan, which was made public on Wednesday. He did not make any changes.

Brazilian daily O Estado de S.Paulo reported on Thursday that Castello Branco was likely to make changes to the plan once in his new role.

The sources told Reuters Castello Branco is also studying moves such as privatizing fuel distribution unit BR Distribuidora SA, a sign he is eager to push ahead with projects welcomed by investors.

Castello Branco previously told Estado de S.Paulo in an interview that BR Distribuidora was not a natural fit for the company and did not generate returns, sending its shares soaring on expectations the government's 70 percent stake could be sold.

Some Petrobras employees are irked by Castello Branco's involvement in company affairs at a time when he does not yet have a formal post, the sources said.

However, one of the sources said Castello Branco's presence in the company did not contravene any governance guidelines. He was learning about Petrobras' internal mechanisms, talking to staff and preparing for his new role, the source said.

"It is the same in Brasilia where they have a (governmental) transition team," the source said. "He is working on the transition."

A representative for Petrobras declined to comment. Castello Branco did not respond to a Reuters request for comment.

Castello Branco recently participated in the firing of an employee associated with Brazil's leftist Workers' Party (PT) at the insistence of Bolsonaro's team, one of the sources said.

Bolsonaro has publicly blamed the PT for dizzying levels of corruption at state-run firms such as Petrobras.

Contacted by Reuters, Petrobras' head of security and intelligence, Regina de Luca, confirmed she had been fired but said she was no longer active politically.

De Luca had served as secretary for public security under former PT President Dilma Rousseff, who was impeached in 2016 for breaking budget rules.

The firing, which shows the tricky political territory that Castello Branco is wading into as he prepares to take the reins at Petrobras, contrasts with the policies of former Petrobras CEO Pedro Parente, who insisted that politics and business should not be mixed at the state-run firm.

(Reporting by Gram Slattery Editing by Tom Brown)