By Bernardo Vizcaino The Islamic unit of Bank Muscat BMAO.OM , Oman&aposs largest lender, plans a dual-currency U.S. dollar and rial sukuk issue worth around $300 million that would be the first sukuk sale by a bank in the country.The issue, which could carry tenors of between three and five years, would be part of a 500 million rial ($1.3 billion) sukuk programme which the bank&aposs shareholders