Before the Russian army launched an invasion of Ukraine on Feb. 24, French war correspondent Loup Bureau was embedded in Donbass, the restive borderland in Eastern Ukraine, which since 2014 has been the site of an ongoing conflict between Russian-backed separatist groups and Ukrainian government forces.

Reports were circulating of an impending Russian attack. Bureau, who had already spent time in the region while shooting his feature-length documentary “Trenches” – screening next week at the Thessaloniki Documentary Festival – expected it to be a localized skirmish. But in the early hours of a full-scale assault that engulfed large parts of the country, the scope of the Russian invasion became clear.

Bureau and other foreign correspondents were on the outskirts of the strategic eastern city of Donetsk. They decided to travel to Kyiv, the Ukrainian capital, some 450 miles away. The journey took two days. “It was very, very difficult. In a matter of hours, there was no fuel in petrol stations. There was no money in the ATMs,” the reporter told Variety. “It was total chaos in every city.”

Bureau spent four days in Kyiv, a city that has come to feel like a second home during nearly six years of reporting from Ukraine. Most of his friends had already left. Others, like his friend and fixer – a Kyiv native who traveled with him to Donbass – decided to continue onward to the relative safety of Western Ukraine.

“He was afraid that the city would be taken by the Russians in the very first days,” said Bureau. “He didn’t even have any clothes” when he left the capital. Frustrated by the logistical challenges, the reporter returned to Paris to regroup.

The events of recent weeks have marked a bloody coda to Bureau’s directorial debut, “Trenches,” which he began developing in 2018. While shooting the film, the director spent four months embedded with Ukrainian soldiers on the frontline of the war in Donbass, where they lived under the constant threat of bombardment from separatist groups under a series of precarious ceasefires that attempted – and failed – to keep the peace.

The film, which premiered last year in the Out of Competition strand at the Venice Film Festival and is being repped internationally by Films Boutique, has found new relevance and urgency as the small-scale conflagration in the separatist Donetsk and Luhansk People’s Republics has now engulfed the whole of Ukraine.

A former Cairo-based correspondent for media including French broadcaster TV5Monde, Bureau’s interest in Ukraine grew out of the 2013-14 Maidan Revolution, a series of peaceful, large-scale demonstrations that ousted the pro-Russian, authoritarian President Viktor Yanukovych. In 2016, he started covering the war in Donbass, a conflict that briefly captured the world’s attention before global interest faded.

Bureau decided to turn to documentary filmmaking instead, finding the form to be better equipped to explore the gray areas of a war many outsiders struggled to comprehend. “The military situation is easy to understand, but sometimes it doesn’t show what the country is going through,” the director told Variety.

Shot in arresting, black-and-white photography, “Trenches” is a powerful depiction of the physical and psychological toll the Donbass War has taken on the young Ukrainians serving on the frontline. As the soldiers struggle to maintain trenches dug decades ago for another generation’s wars, the stark imagery – eerily reminiscent of photos taken on the Western Front during World War I – is a grim reminder of how history continues to repeat itself, even as the world is watching.

Since the current war began, Bureau has stayed in contact with his film’s protagonists. One of the young soldiers is waiting for orders to report to the frontline. Another is hunkered down with her family. A third, who was hospitalized for unrelated health reasons when Russian forces surrounded his city in Eastern Ukraine, told the director he would die fighting.

Bureau expects to return to Ukraine in the next two weeks, though he admitted he was frightened by the scale and ferocity of the current onslaught. Having covered the Arab Spring and its often-bloody aftermath, he described the relentless bombardment by the Russian military as the “most brutal” conflict he’s witnessed as a war reporter.

As with the fighting in Syria, Iraq and elsewhere, the Ukraine war has already displaced millions, in what has become the fastest-growing refugee crisis to hit Europe since World War II. “They are all refugees in their own country. They all need help. But there isn’t much that I can do,” said Bureau. “I feel very helpless.”

For the time being, he said, the one thing he can contribute is what he knows best. “The only thing I can do is try to continue to film and to make people understand what’s happening in this country.”