Images have emerged of bodies found in streets and in yards in the wake of Russian withdrawal from the area following weeks of intense fighting, according to international media reports.

“I am deeply shocked by the images of civilians killed in Bucha, Ukraine,” said Mr. Guterres in a tersely worded statement , which was also posted on his official Twitter account.

“It is essential that an independent investigation leads to effective accountability.”

Osnat Lubrani, UN Humanitarian Coordinator for Ukraine, shared the statement on Twitter.

"Ukrainians are enduring a living hell for more than a month, thousands of civilians have died," she wrote.  "This horrific war needs to stop."

Casualties likely higher

The UN continues to press for an end to the war in Ukraine, which the Secretary-General has described as “unwinnable”.

Conflict began on 24 February, when Russia invaded the country.  Since then, 3,455 civilian casualties have been recorded, according to the latest update from the UN human rights office, OHCHR, published on Sunday.

Of that number, 1,417 persons were killed, and 2,038 injured, though real figures are believed to be considerably higher. 

Most casualties were caused by the use of explosive weapons with a wide impact area, including shelling from heavy artillery and multiple launch rocket systems, and missile and air strikes.

Humanitarian access critical

Posting on Twitter on Friday, Mr. Guterres said the UN “is doing everything in its power to support people whose lives have been overturned by the war in Ukraine.”

Humanitarians have reached more than 1.4 million people, mainly in the east, “but this is not enough” he said. “We need safe, unimpeded access to all areas.”

The fighting has displaced more than 10 million people, both within the country and outside its borders as refugees.

“The speed of the displacement, coupled with the huge numbers of people affected, is unprecedented in Europe in recent memory,” said Filippo Grandi, UN High Commissioner for Refugees, on concluding a visit to Ukraine last week.

To respond to the rising humanitarian needs, the UN and partners launched a $1.7 billion emergency appeal last month to support people in Ukraine and those who have fled abroad.

More than 4.1 million have found shelter in neighbouring countries such as Poland, Slovakia, Hungary, Romania and Moldova, and beyond.

The UN Security Council is scheduled to hold its latest meeting on Ukraine on Tuesday.