The United States has increasingly carried out what have been called freedom of navigation exercises in the South China Sea.

This month, U.S. Defense Secretary Ash Carter visited a warship in the South China Sea in an effort to show America’s commitment to security in the area.

The exercises involve Navy ships and military aircraft. In a freedom of navigation operation, they are sent to areas where other countries have tried to restrict flights or shipping. The aim is to demonstrate that the international community does not accept such restrictions.

The freedom of navigation operations have brought strong reactions from China.

Now, some U.S. lawmakers have called on the Obama Administration to carry out more operations close to artificial islands China is developing in the disputed waterway.

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