After attending the launch ceremony of the Yasref oil refinery, China's largest investment project in Saudi Arabia, President Xi Jinping on Wednesday wrapped up his visit to the kingdom, which was lauded as "historic."

Xi's two-day state visit has witnessed an upgrade of China-Saudi Arabia relations and stepped up energy cooperation between the two countries.

Stepping up energy cooperation

Accompanied by Saudi King Salman bin Abdulaziz Al Saud, the Chinese president attended the ceremony at the King Abdullah Petroleum Studies and Research Center in Riyadh to remotely inaugurate the operation of the Yasref oil refinery, a joint venture between Saudi Aramco and China's Sinopec.

Xi said that energy cooperation between the two countries has brought tangible benefits to both peoples.

The launch of the refinery, he said, conforms to not only the Saudi national development strategy, but also China's strategy of carrying out cooperation with countries in the regions outlined in the China-proposed Belt and Road Initiative, a vision Xi put forward in 2013 to boost interconnectivity and common development along the ancient land and maritime Silk Roads.

As a full-conversion refinery covering 5.2 million square meters in the industrial city of Yanbu on the west coast of Saudi Arabia, Yasref plays a fundamental role in the future of Yanbu industries, the company said.

It is the first overseas refinery Sinopec has built. The two companies signed the agreement in early 2012 with a total investment of nearly 10 billion U.S. dollars. Aramco holds 62.5 percent of the stake while Sinopec holds 37.5 percent.

Energy cooperation is a key element in Xi's visit, during which the two leaders agreed to build stable long-term energy cooperation.

Meanwhile, when meeting with the head of the Cooperation Council for the Arab States of the Gulf (GCC), Xi said that China is willing to carry out comprehensive energy cooperation with the GCC countries and be a long-term, stable and reliable energy market for the six-member bloc.

Saudi Arabia is China's biggest foreign supplier of crude oil and biggest trading partner in West Asia. Two-way trade reached 69.1 billion dollars in 2014, growing by 230 times over that of 1990, when the two countries established diplomatic ties.

Lifting bilateral ties

Reviewing his state visit to Saudi Arabia, Xi said that he was satisfied with the fruitful outcomes, including upgrading bilateral ties and establishing a high-level steering committee for coordinating bilateral cooperation.

Xi held talks with King Salman upon his arrival on Tuesday, and the pair decided to lift bilateral ties to the comprehensive strategic partnership.

"I believe it will deepen the mutual strategic trust, lead to greater achievements in our mutually beneficial cooperation, and help facilitate and broaden our shared interests in international and regional affairs," Xi said on the upgrading of bilateral ties.

The two sides signed a memorandum of understanding on industrial capacity cooperation, agreeing to pursue cooperation under the Belt and Road Initiative, as well as a slew of cooperation deals covering sectors such as energy, communications, environment, culture, aerospace, and science and technology.

China and the GCC also announced that they are committed to working closely to conclude a comprehensive free trade agreement (FTA) within 2016.

During Xi's talks with King Salman, the two leaders welcomed the restart of the China-GCC FTA talks, saying they were "delighted" to see the substantive progress that has been made.

China and the GCC, which includes Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates, began their FTA talks in July 2004, and the process was suspended in 2009.

The two countries also, in a joint statement, made clear their common stances on such regional affairs as Palestine, Syria, Yemen, counterterrorism and the building of a nuclear weapons-free Middle East.

This is the first state visit by a Chinese president to Saudi Arabia in seven years. After leaving Saudi Arabia, Xi Jinping arrived in Cairo on Wednesday for a state visit to Egypt, the second leg of his three-nation Middle East tour which will also take him to Iran.