The US and South Korea have begun a major military exercise in the Sea of Japan, despite threats of retaliation from North Korea. The navy and air force manoeuvres involve 20 ships, 200 planes and 8,000 US and South Korean personnel. Yesterday North Korea threatened to use its nuclear deterrent in retaliation to the exercises.The South Korean defence ministry said the manoeuvres had been relocated from the sensitive Yellow Sea to the Sea of Japan following protests from China, an ally of North Korea.