The United States has warned Iceland that it is deeply concerned about its whaling activities which it says, are posing a great threat to the sustainability of the mammal. The criticism came in a letter from the US Commerce Secretary Gary Locke to the Iceland's Fishing Minister. He said, the US is strongly opposed to Iceland's increasing commercial harvest of whales, in particular, the endangered fin whale. Iceland and Norway are the only two countries in the world which commercially catch whales.