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EPA
Ms Sacayan had been a vocal leader of several organizations seeking equality for Argentina's LGBT community
Argentine President Cristina Fernandez and Amnesty International have called for justice after the violent death of a transgender activist.
Diana Sacayan, a well-known Argentine activist for the rights of lesbians, gays, bisexual and transgender (LGBT) people, was found dead in her Buenos Aires flat on Tuesday.
This is the third violent transgender death in the country in the last month.
Latin America reportedly accounts for the most transgender murders worldwide.
Rights group Amnesty International said on Wednesday that the body of Ms Sacayan showed signs of violence.
"A dark cloud has set over Argentina's trans community," said Mariela Belski, Executive Director of Amnesty International Argentina.
"Unless this latest wave of murders is effectively investigated and those responsible taken to justice, a message will be sent that attacking trans women is actually ok."
President Fernandez echoed Amnesty's concerns.
"I ask the national security services and the metropolitan police to solve this horrible crime," she said during a public address.
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AFP
President Fernandez in 2012 personally gave Ms Sacayan her national identity card recognising her as a woman
Ms Sacayan, 40, had been the leader of a number of organisations seeking equality for Argentina's LGBT community.
In 2012 she was personally given her national identity card by President Fernandez, recognising her as a woman - a first for Argentina.
Ms Sacayan's death followed the killings of Marcela Chocobar and Coty Olmos, two transgender women whose bodies were found over the last month in the provinces of Santa Fe and Santa Cruz.
Latin America accounted for 78% of the 1,731 murders of transgender and gender-diverse people reported worldwide between January 2008 and December 2014, according to activist group Transgender Europe.