Four European leaders made a high-profile visit to show their support for Ukraine on Thursday, denouncing the brutality of the Russian invasion as they surveyed the ruins of a Kyiv suburb that was the scene of intense fighting early in the war and where many civilians were killed.

After arriving in Kyiv to the sound of air raid sirens, the leaders of France, Germany, Italy and Romania headed to Irpin, which was seized and briefly held by Russian troops along with other areas near the capital.

Mass graves have been unearthed in the area, most notably in Bucha, and French president Emmanuel Macron decried the massacres and said there were signs of war crimes.

He denounced the "barbarism" of the attacks that devastated Irpin, and praised the courage of its residents and others in the region who helped thwart Russia's attempt to overrun the capital.

The visit, which includes a planned meeting with President Volodymyr Zelensky, carries heavy symbolic weight given that the three Western European powers have faced criticism for not providing Ukraine with the scale of weaponry that Zelensky has been asking for.

They have also been criticised for not visiting Kyiv sooner. In past weeks and months a number of other European leaders had already made the long trip overland to show solidarity with a nation under attack, even in times when the fighting raged closer to the capital than it does now.

The French president's office said that Macron, German Chancellor Olaf Scholz and Italian Premier Mario Draghi, representing the three largest economies in the EU, travelled to Kyiv together on a special overnight train provided by the Ukrainian authorities.

President Klaus Iohannis of Romania, which borders Ukraine and has been a key destination for Ukrainian refugees, arrived on a separate train, tweeting on arrival: "This illegal Russian aggression must stop!"

"It's a message of European unity for the Ukrainian people, support now and in the future, because the weeks to come will be very difficult," Macron said.

The Russian forces are pressing their offensive in the eastern Donbas region, slowly but steadily gaining ground on the badly outmanned and outgunned Ukrainian forces, who are pleading for more arms from Western allies.

Several air raid sirens rang out while the European leaders were in their hotel preparing for the rest of their visit, and Kyiv authorities urged people to seek shelter. Such alerts are a frequent occurrence.

As he left the hotel, Macron, putting his hand on his heart, said in English: "I want to show my admiration for the Ukrainian people."

German news agency dpa quoted Scholz as saying that the leaders are seeking to show not only solidarity but also their intent to keep up financial and humanitarian help for Ukraine, and a supply of weapons.

Scholz added that this support would continue "for as long as is necessary for Ukraine's fight for independence".

He said that the sanctions against Russia were also significant and could lead to Moscow withdrawing its troops, according to dpa.

Scholz, Macron and Draghi have been criticised not only for helping too little but for speaking to Russian president Vladimir Putin.

Many leaders and regular people in the Baltic and Central European nations, which were controlled by Moscow during the Cold War, believe that Putin only understands force, and have viewed the efforts by Macron and others to keep speaking to Putin following his invasion as unacceptable.

Hopes were high among Ukrainians that the visit could mark a turning point by opening the way to significant new arms supplies.

Tamara Malko, a resident of Pokrovsk, in the Donestsk region of eastern Ukraine, said Macron and Olaf had been "very cold" toward Ukrainians so far, and hoped for a change.

"We want peace very much, vey much and have high hopes for Macron and Scholz," she said. "We want them to see and understand our pain."

Luhansk regional governor Serhiy Haidai said the visit will not bring anything if the leaders ask Ukraine to conclude a peace treaty with Russia that involves giving up territory. He said that is something Ukrainians would never accept.

"I am sure that our president, Volodymyr Zelensky, is not going to make concessions and trade our territories. If someone wants to stop Russia by giving them the territories, Germany has Bavaria, Italy has Tuscany, the French can concede Provence, for instance," he said.

"Listen, this is Russia. These are wild people. Today it will be one territory, tomorrow another one, the day after tomorrow another. And another thing: many heroes of Ukraine died protecting the country as a whole. Nobody will forgive us if people die but we make concessions to the aggressor."

The visit comes as EU leaders prepare to make a decision June 23-24 on Ukraine's request to become a candidate for EU membership, and ahead of an important NATO summit June 29-30 in Madrid.

Also on Thursday, NATO defence ministers are meeting in Brussels to weigh more military aid for Ukraine. On Wednesday, the US and Germany announced more aid, as America and its allies provide longer-range weapons they say can make a difference in a fight where Ukrainian forces are outnumbered and outgunned by their Russian invaders.

On Tuesday, during a trip to Ukraine's neighbours Romania and Moldova, Macron said a "message of support" must be sent to Ukraine before EU heads of state and government "have to make important decisions" at their Brussels meeting.

"We are in a moment where we need to send clear political signals: we, Europeans, we the European Union; toward Ukraine and the Ukrainian people," he said.

Macron is deeply involved in diplomatic efforts to push for a cease-fire in Ukraine that would allow future peace negotiations.

He has frequent discussions with Zelensky and has spoken on the phone several times with Russian president Vladimir Putin since Putin launched the invasion in late February.

Scholz had long resisted travelling to Kyiv, saying he did not want to "join the queue of people who do a quick in-out for a photo opportunity."

Instead, Scholz said a trip should focus on doing "concrete things".

Germany on Wednesday announced that it will provide Ukraine with three multiple-launch rocket systems of the kind that Kyiv has said it urgently needs to defend itself against Russia's invasion.