Taoiseach Micheál Martin has said it was difficult to comprehend the level of cruelty that has been widespread in Ukraine.
Following his visit to the war-torn country, Mr Martin said he was impressed by the resilience of the Ukrainian people, describing his time there as "very emotional".
The Fianna Fáil leader returned to Dublin on Thursday after he spent a day witnessing the devastation inflicted by invading Russian forces in the conflict-scarred suburbs of Kyiv that have borne the brunt of the offensive on the city.
The tour included a sombre visit to the site of a mass grave in the grounds of a church in Bucha.
Mr Martin held a bilateral meeting with Ukrainian president Volodymyr Zelenskiy in the Ukrainian capital.
He said: "We met, first-hand, many communities who have been very traumatised at the level of atrocities that were carried out on their peoples by Russian Federation soldiers in Bucha and Borodyanka.
"It was very difficult to comprehend the level of cruelty and inhumanity that happened and that continues to happen in Ukraine."
Asked what were the lasting impressions of his visit, Mr Martin replied that it is the resilience of the Ukrainian people.
"When you’re in a place like Bucha and you have to visualise the Russian troops were there, which was on the outskirts of Kyiv and that the Ukrainian military and people managed to push them back out again," he added.
"That to me demonstrated extraordinary resilience on behalf of the people of Ukraine.
"And then the needless atrocities and deaths, particularly the deaths of children."
During a visit to a museum, Mr Martin placed a teddy bear at a memorial to the children killed in the conflict.
Mr Martin then visited a memorial commemorating the lives lost in the Holodomor famine in Ukraine in the early 1930s.
"It’s very hard to comprehend how any man can start a war which results in the deaths and the murder of so many children," he added.
"As we left Kyiv last evening, there is an exhibition in the railway which documents the terrible scenes we all saw on our TV screens of thousands and thousands of people fleeing to leave.
"Very, very emotional exhibition."
Mr Martin also said it is "very heartening" to see the EU and the UK working well in its response to the war.
"It’s very clear that they value the range of support that they have had from the European Union and the United Kingdom," he added.
"It brought home to me the importance of our humanitarian response, in terms of our decision very early on, which is very much appreciated by the Ukrainian government, to accept refugees fleeing war, and people who were displaced, fleeing war.
"And also our very strong advocacy for Ukraine to be members of the European Union.
"That was acknowledged and articulated yesterday."
