By Reem Shamseddine KHOBAR, Saudi Arabia, April 10 (Reuters) - Saudi Iron and steel Co (Hadeed), the metals affiliate of Saudi Basic Industries Corp (SABIC), plans to add 4 million tonnes of annual steel output capacity to reach 10 million tonnes by 2025, an executive said. "SABIC's total steel production **w is 6 million tonnes per year ... **w, our ambition for 2025 is around 10 million tonnes. We have to be reasonable - steel is a very tough market," said Abdulaziz al-Humaid, SABIC executive vice-president for metals.