By Lesley Wroughton and Angus McDowall RIYADH (Reuters) - U.S. Secretary of State John Kerry praised Saudi Arabia as a "very, very important" ally on Monday as he visited the Gulf Kingdom on a mission to soothe strains in the relationship over U.S. policy on Iran, Syria and the Palestinian issue. Kerry, who is touring the region, met the Saudi foreign minister on Monday morning and was due to have talks with King Abdullah later. Washington's relationship with the Saudis was crucial as the region faced changes and challenges from the transition in Egypt to civil war in Syria.