Iran has deliberately prolonged talks with the US to try to weaken Donald Trump politically ahead of November's US midterm elections, senior officials say, while fears of renewed military action and deep distrust of Washington have reinforced Tehran's reluctance to strike a quick deal to end the war.

China's military said on Tuesday it had sent forces to watch a US warship that "illegally" entered waters around a disputed shoal in the South China Sea, while further north in the waterway, Taiwan reported a standoff with a Chinese vessel.