South Korea aims to deepen cooperation with the United States, stabilise supply chains with China, and diversify its trading partners to navigate global challenges, its top trade envoy said as the country hosts Asia-Pacific leaders for a trade forum.

It needs the United States for defense and has spent billions building factories in America. But a Trump trade deal this week with China could erase a Korean edge in the U.S. market.

The U.S. will share closely held technology to allow South Korea to build a nuclear-powered submarine, President Donald Trump said ahead of a meeting with China’s leader Xi Jinping.

A US fighter jet and a helicopter crashed into the South China Sea within 30 minutes of each other on Sunday. The F/A-18F Super Hornet and MH-60R Seahawk helicopter, both based off the aircraft carrier USS Nimitz, went down in separate incidents while “conducting routine operations”, said the US navy’s Pacific Fleet.

U.S. President Donald Trump and Chinese President Xi Jinping on Thursday took steps to de-escalate their trade war, swapping some U.S. tariff reductions and tighter export controls for a pause in Beijing's new restrictions on rare earth minerals and magnets and a resumption of its purchases of American soybeans.