NUUK, Jan 16 (Reuters) - Denmark's Joint Arctic Command in Greenland is focused on countering potential Russian activity, not defending against U.S. military threats, its head Major General Soren Andersen said on Friday, amid renewed attention on the Arctic region. U.S. President Donald Trumphas repeatedly described Greenland as vital to U.S. security and has even declined to rule out the use of force to take control of the vast autonomous Arctic island, which is part of the Kingdom of Denmark. "My focus is not toward the U.S., not at all. My focus is on Russia," Andersen told Reuters on board...