Western embassies in Tanzania, including the UK and France, have called on the authorities to release all bodies of those killed in the October electoral violence to their families.
Citing credible reports, the 17 missions said there was evidence of extrajudicial killings, disappearances, arbitrary arrests and the concealment of bodies by Tanzanian authorities during the unrest.
Tanzania has not commented but the statement comes just days after President Samia Suluhu Hassan angrily hit out Western nations, accusing them of interfering in the country's internal affairs.
Hundreds are reported to have been killed in the violence, though the government has not released an official toll.
The authorities violently cracked down on widespread demonstrations after the 29 October presidential election, in which President Samia was declared the winner with nearly 98% of the vote.
Samia's main rivals were barred, prompting widespread anger over the fairness of the presidential contest, which the opposition denounced as a mockery of democracy.
The authorities also imposed an internet blackout and threatened anyone sharing photos from the protests.
Samia has defended the fairness of the election and rejected criticism of her human rights record.
At least 240 people were charged with treason after the protests, but the president later sought to ease tension and asked prosecutors to show leniency. Many of those charged have reportedly already been released.
In a joint statement on Friday, the coalition of Western embassies in Tanzania urged President Samia's government to free political prisoners and allow detainees to get legal and medical help.
They welcomed the government's decision to investigate the causes and circumstances of the violence but stressed that the probe be independent, transparent, and inclusive, involving civil society, faith-based organizations, and political stakeholders.
UN human rights office spokesman Seif Magango mentioned that the Tanzanian government had intensified a crackdown against opponents since the vote and called for the immediate and unconditional release of all those arbitrarily detained.
The US government is reconsidering relations with Tanzania due to the authorities' heavy-handed response against protesters. In a defiant speech, President Samia defended the use of force as necessary against those accusing her of allowing foreign interference in the election.
As political tension continues to rise, the Western nations' demands for accountability and justice in the aftermath of the election have only intensified.
