BEIJING, June 9 -- The 13th round of negotiations over an investment treaty between China and the United States began in Beijing Monday, China's Ministry of Commerce said.

The two sides will step up discussions about "core issues of the texts" during the five-day negotiations, the ministry said in a short statement on its website. The statement did not give details.

Talks over the treaty began in 2008. The two sides held the 12th round of talks in Washington between March 4 and 8 this year.

China and the United States have held substantive negotiations on the texts since the 11th round of negotiations held this year, the statement said.

The negotiations between China and the United States are meaningful for the opening up of mutual investment sectors, protecting and accelerating two-way investment and helping the healthy development of Sino-U.S. economic and trade relations, the statement said.