Pressure mounted on Bangladesh Tuesday after two leading rights activists were hacked to death, the latest in a series of chilling attacks on intellectuals, writers and religious minorities for which only a handful of people have been convicted. At least six men carrying machetes and guns entered an apartment building in Dhaka on Monday night and killed Xulhaz Mannan, editor of a magazine for gay rights, and fellow activist Mahbub Tonoy. Rights groups said the latest killings and the murder on Saturday of a liberal university professor appeared to show the attackers were expanding their range of targets. They demanded justice and greater protection for minority groups in the country. "The brutal killing today of an editor and his friend, days after a university professor was hacked to death, underscores the appalling lack of protection being afforded to a range of peaceful activists in the country," said Amnesty International's South Asia director Champa Patel. "While the Bangladeshi authorities have failed to bring these violent groups to justice, the attackers have expanded their range of targets to now include a university professor and right activists." US Secretary of State John Kerry condemned the killings of Tonoy and Mannan, who worked for the US government aid organization USAID. Both had received threats from militants and hard-liners over their work. "Deplore brutal murder of @USAID local staff member and another Bangladeshi advocate in Dhaka. Those responsible must be brought to justice," Kerry tweeted. In the last month alone, four people have been murdered in Bangladesh for their liberal or secular views, among them a 26-year-old online activist known for his anti-hard-liners opinions. Last year four secular bloggers and a publisher were hacked to death. A number of people belonging to minority communities have also been killed since last year in the country. No one has yet been convicted over those deaths despite a number of arrests. Last year a Bangladesh court sentenced two students to death for the 2013 murder of Ahmed Rajib Haider, the first of a string of attacks targeting secular writers. Another six people were convicted on lesser charges related to Haider's death. The Daesh group has claimed a number of the killings, most recently that of a professor hacked to death in the northwestern city of Rajshahi. A Bangladesh branch of Al-Qaeda has also said it was behind the murders of secular bloggers and writers. But the Bangladesh government rejects those claims and says homegrown Islamist groups are responsible. National police chief A.K.M. Shahidul Hoque said on Tuesday that the attacks bore the hallmarks of attacks by local militants. "The character of the murders is similar to the previous blogger killings. Therefore, it might have been done by the same group," Hoque, said, adding the attack was "planned extensively" and that the victims were followed for days. However, Prime Minister Sheikh Hasina on Monday blamed the main opposition Bangladesh Nationalist Party (BNP) and its ally, Jamaat-e-Islami for the deaths of the two activists and accused the groups of trying to destabilize the country. "The BNP-Jamaat nexus has been engaged in such secret and heinous murders in various forms to destabilize the country," Hasina said. "Such killings are being staged in a planned way." Bangladesh media criticized the government's claims, saying it had a duty to protect minorities whoever was behind the attacks. "It doesn't matter whether they are from transnational terrorist groups like Daesh as they have claimed, or part of locally based militant networks, as the government argues," said the Dhaka Tribune daily in an editorial.