Bangladesh's prime minister has pledged to hunt down and prosecute the attackers who fatally stabbed a gay rights activist and his friend in Dhaka.
Prime Minister Sheikh Hasina blamed the main opposition party and allied militants for Monday night's killings.
However, on Tuesday a different group of radical Islamists claimed responsibility for the attack, raising doubts about her repeated assurances that authorities have the security situation under control.
The stabbings in Bangladesh's capital were the latest in a series of deadly attacks against outspoken atheists, moderates and foreigners.
The victims of the most recent attack were identified as US Agency for International Development employee Xulhaz Mannan, who previously worked as a US Embassy protocol officer, and his friend, actor Tanay Majumder.
Mr Mannan, a cousin of former foreign minister Dipu Moni of the governing party, was also an editor of Bangladesh's first gay rights magazine, Roopbaan. Mr Majumder sometimes helped with the publishing, local media said.
Ansar-al Islam, the Bangladeshi branch of al Qaida on the Indian subcontinent, claimed responsibility in a Twitter message for what it called a "blessed attack".
It said the two were killed because they were "pioneers of practising and promoting homosexuality in Bangladesh" and were "working day and night to promote homosexuality ... with the help of their masters, the US crusaders and its Indian allies".
US Secretary of State John Kerry condemned the "barbaric" murders in a statement on Monday and said the US government would support Bangladeshi efforts to bring the perpetrators to justice.
Police said no arrests have been made in the attack, which involved at least five young men who posed as courier service employees to gain access to Mr Mannan's apartment building.
After the attack, a crowd in the area and patrolling police chased the attackers, senior police official Shibli Norman said.
"Some people chased the attackers, thinking they were robbers," but did not catch anyone, Mr Norman said.
A policeman briefly caught one of the attackers but was injured when the man hit him with a sharp weapon and fled, he added.
A security guard working at the building said he was injured when one of the men hit him with a knife while fleeing.
Crime scene investigators recovered a mobile phone and bag apparently left by the attackers.
The national police chief, AKM Shahidul Hoque, expressed confidence the group would be caught.
"We have found some evidence," he said.
Sheikh Hasina quickly blamed the radical Jamaat-e-Islami group and its political ally, the opposition Bangladesh Nationalist Party.
"Everybody knows who is behind these killings," she told party MPs in a meeting on Monday night after the attacks, which came just days after a professor of English was hacked to death on the street of a north-western city.
Repeating the government's usual accusations, Sheikh Hasina said the opposition was orchestrating the attacks to destabilise the country and upset her secular rule, while also retaliating against the government's efforts to prosecute war crimes committed during the country's 1971 war of independence.
The opposition denies the allegations, saying they are being made into scapegoats for her failure to maintain security and placate the country's desire for Islamic rule.
The US government and numerous rights groups have lambasted Sheikh Hasina's government for failing to keep civil society safe.
Earlier this month, the US said it was considering granting refuge to a select number of secular bloggers facing imminent danger in Bangladesh.
State Department spokesman John Kirby said that remained an option, while describing Mr Mannan as a "beloved member of our embassy family and a courageous advocate" for gay rights, and pledging US support to Bangladeshi authorities "to ensure that the cowards who did this are held accountable".
Amnesty International noted that Bangladesh considers homosexual relations a crime, making it harder for gay activists to report any threats against them.
The group's South Asia director, Champa Patel, said the attack "underscores the appalling lack of protection being afforded to a range of peaceful activists in the country".