China pledges constructive role in peace efforts as it calls US blockade of Iranian ports "dangerous and irresponsible". Also on East Asia Tonight: Chinese exports stutter in March over uncertainties in the Middle East. Also, Vietnam leader To Lam visits Beijing in first official trip as head of state and Communist Party chief. 00:00 Headlines 01:34 China's Xi Jinping pledges constructive role in US-Iran peace talks 07:35 South Korea warns of prolonged energy disruptions 08:44 Vietnamese