The number of refugees fleeing Ukraine since Russia launched a war on its neighbor has crossed 2.5 million, the UN refugee agency said on Friday.

"The UN estimates that there are now at least 2 million internally displaced people," in Ukraine, UNHCR spokesman Matthew Saltmarsh said at a news conference at Ukraine's border with Poland.

"The total number of refugees has just passed 2.5 million ... an unprecedented flow of people in Europe, certainly the most since the World War II."

UNHCR said that some of the refugees face the danger of landmines while fleeing.

"We have so far recorded 564 civilian deaths and 957 injuries since the armed attack began on Feb. 24, although the actual figure could be much higher," said Elizabeth Throssell, UN Human Rights Office spokesperson.

"Civilians are being killed and maimed in what appear to be indiscriminate attacks, with Russian forces using explosive weapons with wide-area effects in or near populated areas," said Throssell.

These include missiles, heavy artillery shells and rockets, as well as airstrikes.

The rights office spokesperson said that schools, hospitals and kindergartens had been hit – with hugely devastating consequences.

She said that on March 3, 47 civilians were killed when Russian airstrikes hit two schools and several apartment blocks in Chernihiv, northern Ukraine.

"On 9 March, a Russian airstrike hit Mariupol Hospital No.3, injuring at least 17 civilians. We are still investigating reports that at least three civilians may have been killed in the airstrike," said Throssell.

Mariupol hospital attack

She said her office spoke to different sources in Mariupol, including local authorities, consistently indicating that the hospital was clearly identifiable and operational when hit.

The rights office also has received credible reports of several cases of Russian forces using cluster munitions, including in populated areas.

On Feb. 24, a cluster munition exploded at the Central City Hospital in Vuhledar, in Ukraine’s breakaway Donetsk region, killing four civilians, injuring 10 others, and damaging ambulances, civilian vehicles, and the hospital itself.

"There were other cluster munition attacks in several districts of Kharkiv, in which nine civilians were killed and 37 injured," Throssell said.

"We remind the Russian authorities that directing attacks against civilians and civilian objects, as well as so-called area bombardment in towns and villages and other forms of indiscriminate attacks, are prohibited under international law and may amount to war crimes."

The World Health Organization's Tarik Jasarevic said at the news conference that there had been 26 attacks on healthcare facilities in Ukraine reported since the war.

"There were just reports this morning from Kharkiv authorities that a psychiatric institute has been attacked. If this proves to be true, this would be yet another attack on health in Ukraine.

"So we condemn all attacks on health care, whether it is health care facilities, health care personnel, or patients. This is in flagrant violation of international humanitarian law; it deprives people of access to health care; it puts in danger the lives of patients and health care workers."

Russia's war on Ukraine, which began on Feb. 24, has drawn international condemnation, led to financial sanctions on Moscow, and spurred an exodus of global firms from Russia.