China's land reclamation around reefs in the disputed South China Sea is undermining freedom and stability and risks provoking tension that could lead to conflict, U.S. Deputy Secretary of State Antony Blinken told a press conference in Jakarta.

China claims 90 percent of the South China Sea, which is believed to be rich in oil and gas, despite overlapping claims by Brunei, Malaysia, the Philippines, Vietnam and Taiwan.

Recent satellite images suggest that China has made rapid progress in filling in land in contested territory in the Spratly Islands and in building an airstrip suitable for military use and that it may be planning another.

“As China seeks to make sovereign land out of sandcastles and redraw maritime boundaries, it is eroding regional trust and undermining investor confidence,” Blinken said on Wednesday.

“Its behavior threatens to set a new precedent, whereby larger countries are free to intimidate smaller ones, and that provokes tensions, instability and can even lead to conflict.”

The United States and China clashed over the dispute on Saturday, when visiting U.S. Secretary of State John Kerry urged China to take action to reduce tension. China said its determination to protect its interests was “as hard as a rock.”

Asked about Blinken's remarks, China's Foreign Ministry demanded on Thursday that the United States not take sides on South China Sea claims and said his comments damaged trust in the region. “The U.S. assumptions are groundless,” ministry spokesman Hong Lei said at a regular news briefing.

Blinken said the previous day that competing claims had to be handled “diplomatically.”

“Comments of this sort are not good for the solving of tensions and are not beneficial for the mutual trust between countries as well as maintaining the peace and the stability of the South China Sea region,” Hong said.

Because of the territorial disputes, many consider the area one of Asia's most potentially dangerous hot spots.

Reuters