DHAKA (AFP) - Hundreds of protesters in Bangladesh threw petrol bombs at police on Tuesday as opposition parties enforced a nationwide strike demanding elections under a neutral caretaker government. As a top US official voiced concern about levels of violence in the country, there were reports of clashes in several big cities, including the capital Dhaka. The worst unrest was seen in the northwestern city of Rajshahi where police fired rubber bullets at demonstrators after coming under attack from youths hurling Molotov cocktails.