Al-Rajhi Bank, the Kingdom\'s biggest Islamic lender, on Tuesday posted an 18 percent rise in first-quarter net profit due to an increase in operational income, but it missed analysts\' forecasts. Earnings for the three months ended March 31 rose to SR2.01 billion from SR1.70 billion a year earlier, the bank said in a statement posted on the website of the Saudi bourse.   The bank had net profits of SR1.9 billion in the last quarter of 2011. Operational income rose 16.7 percent to SR3.43 billion, net income from finance and investments rose 4.3 percent to SR2.33 billion and total assets at the end of the period were SR234 billion, compared to SR203 billion a year earlier.