UNITED NATIONS, March 19 (Reuters) - U.N. Secretary-General Kofi Annan called on Friday for a broad independent probe into the U.N.-administered Iraq oil-for-food program, saying it was "highly possible" there had been a lot of wrongdoing. Annan, in his first comments on the burgeoning allegations, has been under pressure to conduct an investigation into corruption from Iraqi leaders as well as the U.S. officials searching for former President Saddam Hussein's hidden assets. The United Nations has begun an in-house probe of its own staff but Annan stressed a wider, independent investigation was needed to cover outside firms and individuals. This...