Dhaka, June 21 -- The World Bank said Thursday it is worried that some countries are less and less transparent about their public debt and use complex borrowing tools, making it harder to measure how much they owe.To remedy this the bank called for a fundamental change in the way debtor and creditor countries report and disclose debt.The worries concern in particular low-income countries that make increasing use of borrowing arrangements the bank considers opaque.These include private placements - a kind of funding round done not publicly but privately, central bank swaps, and collateralized transactions, the bank said in a report on debt transparency.The proportion of low-income countries publishing some debt data has grown from below 60 p...