Authorities in Bucha say that more than 400 people have so far been found dead in the city since Russian forces withdrew from the area.
The process of identifying bodies buried in mass graves is now under way.
Fianna Fáil Senator Timmy Dooley and MEP Billy Kelleher recently returned to Ukraine at the invitation of President Volodymyr Zelensky's Servant of the People Party to witness the atrocities in their capacity as members of the EU Alliance of Liberals and Democrats for Europe.
Speaking on RTÉ's Six One News from Kraków Airport on his way home from Ukraine, Mr Dooley outlined what he had witnessed there.
He said: "To say that the region has been devastated is an understatement.
"Houses have been bombed, they have been taken down by tanks. They've been set fire to, they've been ransacked, they have used shells and all sorts of mortars to destroy these citizen's homes.
"This was an attack on civilians and you know the Russian Federation would have you believe that this kind of stuff is a figment of the imagination of the Western world. Well, I can tell you, from my perspective it is not."
We need your consent to load this rte-player contentWe use rte-player to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage Preferences
Mr Dooley said that innocent civilians have been targeted in the most inhumane way.
"These are war crimes that have been perpetrated on Ukrainian citizens, individuals who have not been involved in the war whatsoever, there were no military targets in the region.
Yesterday, the two men were taken to the site of a mass grave where investigators were excavating.
"[They were] removing bodies from the ground, beginning the painstaking work of identifying them and attempting to build the case, which hopefully will be prosecuted against Putin at a later stage.
"To witness that really is something that in this day and age you would have thought is something that is confined to history but sadly it hasn't been," Mr Dooley said.
They also encountered people returning to the shells of their homes, who were trying to see if there was anything left for them to salvage from the ruins.
Mr Dooley said that although entire blocks and villages will have to be demolished, the people whose lives and livelihoods have been destroyed are remarkably resilient.
He said: "These people are resilient though. I met an elderly couple who have been there all their lives and they took us into what is the burnt wreck of their home.
"Obviously it was very emotional for them. It was their first time going back, but they want to see their home rebuilt, they want to live in this area."
He explained that more sanctions are required in order to stop funding Mr Putin's war machine.
Mr Dooley said: "I think it says to all of us that we must maintain our resolve and ensure that we must try to bring Europe together to work against this. And that will require further sanctions.
"It was said to us by everyone we met yesterday at official level that Europe has to ensure that we put in place the ultimate sanctions.
"That we wean ourselves off the oil and gas and coal that on a daily basis provides €1 billion to the Russian war machine, that's what's driving this.
"Until such time as we, from a European perspective, come together at European Council level and effectively bring these sanctions to the ultimate conclusion, to wean ourselves off that amount of their energy and deprive them of the funding that they are using to wage this war."
Meanwhile, French forensic experts have arrived in Bucha near Kyiv to help Ukraine authorities establish what happened in the town where hundreds of bodies have been discovered since Russian forces withdrew.
Ukraine says the people were killed by Russian forces during their occupation of the area.
Reuters has not been able to verify the number of people found dead in Bucha or the circumstances of their deaths.
The discovery of so many slain civilians in Bucha after the Russian withdrawal has provoked a global outcry.
Russia has denied responsibility and dismissed allegations its troops committed war crimes as fake news.
As the group from the French Gendarmerie's forensic science department looked on, workers in hazmat suits dug earth from a shallow grave and lifted out a heavy mass wrapped in an orange blanket.
Prosecutor General Iryna Venediktova said, citing witnesses, that the burnt body parts inside were those of a woman and her two children.
Ms Venediktova said over the next couple of weeks the French experts would help the Ukrainian authorities establish what happened to the people in Bucha.
"We have now a lot of jobs unfortunately with war crimes," Ms Venediktova said at the churchyard site, where locals hastily buried people who died during the town's occupation.
"When you see dead bodies here, from the other side, from the Russian Federation, they say it is all fake, all this is our theatre," Ms Venediktova said.
She said the international experts would be able to see the situation for themselves.
"They can see everything, they can see the situation here: real graves, real dead bodies, real bomb attacks. That's why for us this moment is very important."
Moscow, which has repeatedly denied targeting civilians since its 24 February invasion of Ukraine, has called allegations that Russian forces executed civilians in Bucha while they occupied the town a "monstrous forgery" aimed at denigrating the Russian army.
Russian President Vladimir Putin said today that images and footage of dead bodies strewn across the Ukrainian town of Bucha were fake.
Additional reporting Reuters
