China plans to cooperate with Saudi Arabia and other Gulf countries in the fields of nuclear energy, nuclear security and space exploration, President Xi Jinping said on Friday, showcasing his nation's strengthening ties with a region that was once firmly in the U.S. sphere of influence. Mr. Xi was speaking in the Saudi capital, Riyadh, at a summit with rulers and officials from the six Gulf Cooperation Council countries -- Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, and the United Arab Emirates -- during a three-day visit to Saudi Arabia. Later on Friday, he held his third and final summit of the visit with other Arab and African leaders. Both China and Saudi Arabia described Mr. Xi's visit this week as a historic event ushering in a new era of relations between Beijing and the Middle East, a region that once had a mainly oil-based relationship with China, a major consumer of the Gulf's fossil fuel exports. Arab states are increasingly building broader ties with China that extend into arms sales, technology transfers and infrastructure projects.