THE first US visit by a Chinese head of state after more than a decade has heralded a diplomatic thaw, with Washington offering Beijing more atomic power reactors costing several billion dollars; in exchange, China is said to have promised in writing that it would sever nuclear ties with Iran and even perhaps with Pakistan. Striking the last-minute deal, US President Bill Clinton said: "This is a win, win, win agreement. It serves American national security, environmental and economic interests."