METALS-Aluminium hits 6-1/2-year peak on supply worries; nickel rallies

(Updates prices) By Manolo Serapio Jr MANILA, April 18 (Reuters) - London aluminium futures rose to their strongest level since 2011 on Wednesday amid growing worries over tighter supply, while nickel surged more than 4 percent to a three-year peak. U.S. sanctions on major aluminium producer Rusal have pushed aluminium prices by more than 20 percent since the sanctions began earlier this month. Some traders and analysts were puzzled about the sudden spike in nickel prices, with some