Uganda's Anti-Homosexuality Act signed into law in May
'We cannot turn away from abuses'
U.S. Ambassador to the U.N. Linda Thomas-Greenfield chaired Monday meeting
Activists from Colombia, Afghanistan expected to speak at March 20 gathering
President stressed 'fundamental freedoms' at risk around the world
Victor Madrigal-Borloz traveled across country in August
Linda Thomas-Greenfield says LGBTQ rights remain a top priority
