China and Vietnam continued a dispute over a Chinese oil rig in the South China Sea on Thursday, with the former acknowledging for the first time its use of water cannons as a method of deterring Vietnamese ships.

A foreign ministry official in Beijing called for Vietnam to remove their ships from the area southwest of the Paracel Islands in the South China Sea. Those islands are controlled by China but also claimed by Vietnam and Taiwan. The dispute reached its most contentious point over the weekend when, according to South Korean officials, Chinese vessels used water cannons and rammed ships, damaging two South Korean ships and injuring six. China characterized its use of water cannons as the “utmost restraint,” and said on Thursday that Vietnamese ships had rammed theirs as many as 171 times during the week.

About 35 Vietnamese ships and 80 Chinese ships are in the area of the oil rig, China’s first deep sea drilling platform. The structure is a large part of China’s increasing possessiveness over what are characterized as “core interests,” according to the Times—interests which are non-negotiable.

The scuffle comes in the midst of a lot of peacocking from China and the United States. Last Week, President Obama announced an increased military presence in Asia while China also continues to assert control over much of the South China Sea.