KUALA LUMPUR, Feb 27 (Reuters) - Malaysia's Prime Minister Najib Razak announced on Monday that Saudi Arabia's state oil company will invest $7 billion into an oil refinery to be set up by Malaysian oil company Petroliam Nasional Bhd (Petronas).

Najib said the decision was made before noon on Monday after discussions between top executives from Petronas and Saudi Aramco to build the plant, part of Malaysia's Refinery and Petrochemical Integrated Development (RAPID) project in Pengerang in the southern state of Johor.

(Reporting by Rozanna Latiff; Editing by Christian Schmollinger) ((Joseph.Sipalan@thomsonreuters.com; +60323338019; Reuters Messaging: joseph.sipalan.thomsonreuters.com@reuters.net))