The flagship newspaper of China's ruling Communist Party has warned Washington that there will be a "price" to pay if it crosses China's "bottom line" by meddling in disputes over the South China Sea.

The People's Daily editorial Wednesday comes as Beijing ramps up efforts to assert its stance ahead of a ruling by an international tribunal in a case filed by the Philippines challenging China's claims to most of the South China Sea. China is boycotting the case before The Hague-based court and says it will not accept the verdict.

The paper said that bilateral ties and regional stability were at stake and that the U.S. should recognize that "there is a bottom line with every issue, and a price will be paid if that line is crossed."