WARSAW (Reuters) -Poland's newly appointed prime minister, Donald Tusk, said on Tuesday his country will demand the full mobilisation of the West to help Ukraine, adding it will regain a leadership position in Europe and will be a strong part of NATO. Poland's parliament backed Tusk to become prime minister on Monday, ending eight years of nationalist rule and putting the country on track for a thawing of relations with the European Union. Tusk, a former European Council president, will face a vote of confidence later on Tuesday.