The United States is not looking for conflict with China but steps it is taking in the South China Sea are self-isolating and prompting other countries to seek help from Washington, US Defense Secretary Ashton Carter said on Friday.

The deployment of autonomous weapons would represent a dangerous new era in warfare, scientists said.

The United States wants the United Nations to raise funding for refugees this year by 30 per cent to $13 billion and says it will ask for the extra cash at a summit to be hosted by President Barack Obama in September.