Suspected Islamist militants armed with knives hacked a Bangladeshi gay activist and his friend to death Monday.
The activist, Xulhaz Mannan, also worked for United States Agency for International Development (USAID) and "was affiliated with the U.S. Embassy," said State Department spokesman John Kirby.
"We don't know the motivation here ... nobody has claimed responsibility for this," Kirby said. "We do know is that he was a staunch defender of LGBT rights."
Kirby did not identify the man who died with Mannan in the "barbaric attack."
"Xulhaz was more than a colleague to those of us fortunate to work with him at the U.S. Embassy," Marcia Bernicat, the U.S. Ambassador to Bangladesh, said earlier in a statement. "He was a dear friend. Our prayers are with Xulhaz, the other victim, and those injured in the attack."
The White House also condemned the murder of Mannan, calling him "a voice for justice, equality, and human rights for all."
"Mr. Mannan set an example of dignity, courage and selflessness, and his legacy will live on in the causes he championed," Ned Price, spokesman for the National Security Council, said in a statement.
Mannan worked as a protocol specialist at the U.S. embassy for eight years before joining USAID last September, where he worked "tirelessly to support organizations focused on broadening and deepening political understanding throughout Bangladesh."
"He was the kind of person willing to fight for what he believed in, someone ready to stand up for his own rights and the rights of others," USAID said in a statement.
Mannan, 35, was also the editor of Roopbaan, the conservative Muslim country's only LGBT-oriented magazine. He is survived by his mother, his brother, and "friends in Bangladesh and around the world," USAID said.
The activist was murdered two days after a university professor was killed in a similar fashion in an attack claimed by ISIS.
Mannan was lured to his death by an attacker posing as delivery driver who summoned him to the entrance of his building in Dhaka, a local Bangladeshi detective on the case told NBC News.
When Mannan and his friend arrived, five other men rushed out and attacked them, he said. At least one of the guards assigned to the building were injured when they tried to intervene.
Bangladesh has seen a surge in violent attacks over the past few months that targeted liberal activists, members of minority Muslim sects, and other members of other religious groups.