Taoiseach Micheál Martin witnessed the devastation inflicted by invading Russian forces as he visited areas of Kyiv that have borne the brunt of the offensive on the city.
Mr Martin is in the Ukrainian capital where he held talks with president Volodymyr Zelenskiy.
The leaders met in Mr Zelensky’s heavily fortified offices in the city to discuss the war and Irish and EU efforts to support Ukraine in the face of ongoing Russian aggression.
In a speech in Kyiv on Wednesday, Mr Martin said he wished to express Ireland’s solidarity with the people of Ukraine.
“We admire you and we are with you. Russia’s brutal war against this beautiful, democratic country is a gross violation of international law. It is an affront to everything that Ireland stands for. It cannot and it will not be allowed to stand,” Mr Martin said.
The Taoiseach paid tribute to President Zelenskiy on achieving EU candidate status, saying “Ukraine belongs to the European Union” and that Ireland would “be with you every step of the way and we’ll do what we can to help”.
Prior to the talks with the Ukrainian president, Mr Martin visited a museum in Kyiv that is exhibiting items from the war, including damaged Russian military vehicles and missile fragments.
He placed a teddy bear at a nearby memorial to the children killed in the conflict so far.
Mr Martin then visited a memorial commemorating the lives lost in the Holodomor famine in Ukraine in the early 1930s.
The Taoiseach placed a wreath at the site and later lit a candle in an underground part of the memorial.
He began a trip to Kyiv by viewing the conflict-scarred suburbs of Borodyanka, Bucha and Irpin.
The tour included a sombre visit to the site of a mass grave in the grounds of a church in Bucha.
Mr Martin is using the visit to Kyiv to reiterate Ireland’s solidarity with the Ukrainian authorities in the face of the Russian invasion.
His day-long itinerary in the war-torn city began with a trip to Borodyanka – a town on the outskirts of Kyiv that has suffered widespread damage under Russian shelling.
On the 30-minute drive from the railway station, the Taoiseach passed Hostomel airport, where his convoy stopped to observe a demolished bridge.
The delegation also drove past bombed-out warehouses, shopping centres and petrol stations.
The scale of Ukrainian efforts to defend their capital was evident, with numerous bunkers and fortifications visible on the journey.
In Borodyanka, Mr Martin met the town’s mayor and viewed apartment blocks gutted by fire during the Russian bombardment.
From there, Mr Martin visited the site of a mass grave in Bucha. The grave was discovered in the grounds of the church of St Andrew.
A local cleric showed Mr Martin the site and an associated exhibition of graphic photographs of exhumed bodies and pictures of civilians left dead on the streets of the suburb when Russian forces retreated.
The Irish delegation then travelled to nearby Irpin where the Taoiseach was shown badly-damaged apartment blocks that had been hit by Russian shells.
Afterwards, Mr Martin said: “It is difficult to comprehend the devastation and inhumanity of Russia’s attacks on Irpin, Borodyanka and Bucha.
He said it was “clear how important it is for women and children to get to Ireland to escape trauma and brutality. We stand with Ukraine.”
Mr Martin said Ireland will stand with Ukraine in the face of Russia’s “immoral and unprovoked war of terror”, in advance of his arrival in Kyiv on Wednesday morning.
He will engage with Ukrainian authorities on how Ireland and the EU can support the country’s current and future needs.
Speaking in advance of his visit, Mr Martin said: “The bombardment and attacks on civilians are nothing short of war crimes, and I will use my visit to express Ireland’s support for moves to hold those behind these attacks fully accountable.
“The spirit and resolve of the Ukrainian people has inspired us all, and Ireland will provide every support for Ukraine’s path to full EU Membership, and continue to welcome and support civilians fleeing this war.”
Mr Martin was invited to Ukraine last month by Mr Zelenskiy, who also singled him out for thanks after the European Council approved Ukraine’s bid for candidate status at a recent summit in Brussels. Mr Martin was a strong early supporter of Ukraine’s bid for membership of the EU.
He will become the latest in a series of western leaders to visit the Ukrainian capital since Russia’s invasion of the country in late February.
It also comes after Mr Putin on Monday declared victory in seizing the eastern Ukrainian province of Luhansk, with his troops escalating their offensive in neighbouring Donetsk.
Mr Martin has warned previously that the Russian president appeared to be leveraging its natural gas supplies to exert maximum pressure on Europe ahead of the winter period.
Ireland has also taken in more than 36,000 Ukrainian refugees since the beginning of the Russian invasion.
The Irish State has given €20 million in humanitarian support and assistance to the country, as well as health equipment and medical donations worth more than €4.5 million.
Minister for Foreign Affairs Simon Coveney visited Kyiv in April and Mr Zelenskiy has also addressed the Oireachtas by video-link, praising the Irish people’s support for his country. – Additional reporting PA