Saudi King Salman on Wednesday appointed Saudi Aramco Chief Executive and President Khalid al-Falih as the country's health minister and chairman of the state oil company in the world's top crude exporter, state television said.

Falih's replacement as head of Aramco, which he had led since January 2009 after a 30-year career in the company, was not immediately named.

The move was part of a major reshuffle that also saw King Salman appoint Interior Minister Mohammed bin Nayef as his new heir, replacing the monarch's half brother Prince Muqrin.

The post of Aramco chairman had been held by Oil Minister Ali al-Naimi, himself a former chief executive of the company, who stayed in the ministerial position he has occupied for 20 years. Falih has long been considered a possible successor of Naimi as oil minister.

Falih has created new business units at Saudi Aramco and planned to widen the company's focus from crude production to emphasise its role in producing gas, chemicals and refined products, and renewable energy.

An annual corporate report is due this week which outlines the achievements of Aramco for the past year.

The position of health minister is important in Saudi Arabia as it has been imposing stricter preventive measures against the spread of Middle East Respiratory Syndrome (MERS), which emerged in 2012 in the kingdom and has killed hundreds.