Defense secretary James Mattis has warned the US will not accept China’s militarization of man-made islands in the South China Sea.

Speaking at a security conference in Singapore, he said such moves undermined regional stability.

At the same time, Gen Mattis praised Beijing’s efforts to restrain North Korea’s missile and nuclear activity.

His comments came shortly after the UN Security Council expanded targeted sanctions against North Korea in response to a series of missile tests conducted this year.

Mattis also said the United States welcomed China’s Economic development, but he anticipated “friction” between the two countries.

He added that “Extremist Groups” must be defeated not only in Iraq and Syria but also in Southeast Asia, and that the U.S. was working to encourage nations in the region to contribute sufficiently to their own security.