By Lamine Chikhi

ALGIERS, March 20 (Reuters) - Algerian state energy firm Sonatrach has replaced Chief Executive Amine Mazouzi after less than two years in the job with Abdelmoumen Ould Kadour, the energy ministry said on Monday.

The surprise decision comes at a sensitive time for Sonatrach and Algeria, which began to increase oil and gas production last year after a prolonged period of stagnation and a lack of major foreign investment.

A statement from the ministry gave no reason for the change. Ould Kadour is an engineer who graduated from the Massachusetts Institute of Technology and headed U.S.-Algerian firm Brown & Root Condor in the 1990s.

Before Mazouzi's appointment in May 2015, the energy giant went through turbulent times with five CEOs in five years, shaken by a corruption scandal, weak foreign oil interest in energy bids and pressure from the drop on crude prices.

Just a day before the announcement, Mazouzi hosted the CEO of Eni at a southern oilfield where the two discussed the Italian company's commitment to Algerian investment.

Algeria remains dependent on oil and gas earnings which provide 60 percent of the state budget and Sonatrach's performance is key to the health of the economy.

The North African OPEC member nation had struggled to attract oil investment because of tough terms that made foreign firms wary, but in 2016 Sonatrach began to take a more flexible approach to bilateral talks with foreign partners.

But there have been divergent views within Algeria's ruling elite over how hard to push for foreign investment and domestic economic reform to boost revenues and spur growth.

In the statement, Energy Minister Noureddine Boutarfa called on Ould Kadour to "act with full responsibility and confidence to put in place the qualitative changes that allow Sonatrach to evolve and prosper in a calm business climate".

The sharp fall in oil prices hit Algeria hard, prompting the government to look at more flexible ways to improve revenues. Algeria's energy revenues were $27.5 billion in 2016, less than half the $60 billion it earned in 2014.

(Writing by Aidan Lewis; editing by Dale Hudson and David Clarke) ((Aidan.Lewis@thomsonreuters.com ; +216-29850352;))