China has offered to invest USD 3.7 billion in Sri Lanka, stated to be the biggest-ever foreign investment in the island nation, to build a state-of-the-art oil refinery as the two countries signed a new plan to upgrade BRI cooperation during Sri Lankan President Anura Kumara Dissanayake's state visit here. On Thursday, Dissanayake met Chinese Premier Li Qiang and Chairman of the Standing Committee of the National People's Congress Zhao Leji and pitched for more Chinese investment in his address to Chinese firms. A day earlier, Dissanayake held talks with his Chinese counterpart Xi Jinping following which the two sides signed 15 agreements.