* Group says more than 100 rapes documented under quasi-civilian government
* Many of attacks were gang rapes and 28 women died, it says
* Government denies allegation, says it acts against offenders
By David Brunnstrom
WASHINGTON, Jan 14 (Reuters) - A women's group says the military in Myanmar is still using rape as a weapon of war, with more than 100 women and girls raped by the...