Rights group Amnesty International said it fully stood by its accusations that Ukraine was endangering civilians by establishing bases in residential areas to counter the Russian invasion.
It follows a report published yesterday that prompted a furious response from Kyiv.
Amnesty "fully stands by our research," the organisation's Secretary General Agnes Callamard told AFP in emailed comments.
"The findings... were based on evidence gathered during extensive investigations which were subject to the same rigorous standards and due diligence processes as all of Amnesty International's work," she added.
The human rights group accused Ukrainian forces of violating international law and endangering civilians by establishing bases in residential areas, including in schools and hospitals.
Amnesty International Ireland confirmed that "two or three" members had been in contact to express their "negative feelings" about the Ukraine report.
It said these members had threatened to withdraw their membership from the organisation.
The Irish branch of the human rights group said it will be passing on this feedback to Amnesty headquarters.
In its report, Amnesty listed incidents when Ukrainian forces appeared to have exposed civilians to danger in 19 towns and villages in the Kharkiv, Donbas and Mykolaiv regions.
"We have documented a pattern of Ukrainian forces putting civilians at risk and violating the laws of war when they operate in populated areas," Ms Callamard said.
"Being in a defensive position does not exempt the Ukrainian military from respecting international humanitarian law."
Residential areas where Ukrainian soldiers based themselves were miles away from frontlines, and "viable alternatives" were available that would not endanger civilians, the report said.
But it said the soldiers had failed to tell civilians to evacuate the areas, despite launching strikes on Russian forces that exposed them to retaliatory fire.
Amnesty researchers witnessed Ukrainian forces using hospitals as "de facto military bases" in five locations and in 22 schools.
Although the schools have been shut during the conflict, they were located in civilian neighbourhoods.
"We have no say in what the military does, but we pay the price," the report quoted one resident as saying.
The findings prompted an angry response from Kyiv.
Amnesty had tried to "shift the responsibility from the aggressor to the victim", Ukrainian President Volodymyr Zelensky said yesterday evening.
"There is no condition, even hypothetically, under which any Russian strike on Ukraine becomes justified. Aggression against our state is unprovoked, invasive and terrorist.
"If someone makes a report in which the victim and the aggressor are supposedly equal in some way, if some data about the victim is analysed, and the aggressor's actions at the same time is ignored, then this cannot be tolerated," he added.
Ukraine's Foreign Minister Dmytro Kuleba branded the allegations "unfair".
"This behaviour of Amnesty is not about finding and reporting the truth to the world, it is about creating a false equivalence - between the offender and victim, between the country that destroys hundreds and thousands of civilians, cities, territories, and a country that is desperately defending itself," he said.
Defence Minister Oleksiy Reznikov called the report a "perversion" as he said it questioned the right of Ukrainians to defend their country.