On the perilous journey to the front line, there are few Ukrainians who could convince the Russians to let their guns fall silent.

But as Andriy Pasternak trudges towards the fierce fighting, bombarded by mortar fire, he does just that with a single phone call.

Stop the fighting, we’ve got a job to do, he tells his Russian counterpart.

Within minutes, the bombs stop falling and Mr Pasternak edges his way to the waiting Russians for negotiations that will eventually return 175 Ukrainian prisoners of war and seven captive civilians to their families in time for Easter.

Mr Pasternak is one of a small band of Ukrainian negotiators involved in direct talks with their Russian enemies, risking their lives to do so.

Unlike his contemporaries involved in high-profile negotiations to bring about a ceasefire from the comfort of glitzy hotels, Mr Pasternak must travel through drone-infested kill zones to bring back prisoners of war.

There is little known about the process behind the exchanges, which feature direct talks between Ukrainian and Russian officials, as well as help from foreign governments, such as the United States or Middle Eastern countries.

But in a rare interview with a Western outlet, Mr Pasternak was able to lift the lid on how he communicated with Russian commanders via text message before organising mini-ceasefires to meet them on the front line to facilitate the swaps.

As head of the Security Service of Ukraine’s joint centre for the search and release of prisoners of war, he was uniquely placed to tell the story.

“It can be using messenger apps, like WhatsApp or whatever,” he told The Telegraph, describing his interactions with Russian counterparts.

“But it can also be a face-to-face meeting at the combat clash.”

Such huddles are dangerous, with officials from both sides having to travel through large kill zones flooded with drones, artillery and other deadly weapons.

Mr Pasternak said the negotiations could happen anywhere: Donetsk in the east, Kherson in the south or Chernihiv in the north.

While his colleagues have failed to secure a wider truce, he is able to broker mini-ceasefires, or a “silent mode for 500m”, to conduct the talks.

It is one area where Ukrainian officials have had a degree of success when dealing with their often tricky and deceptive Russian counterparts.

A month before the 182 prisoners were returned home in time for Orthodox Easter, Mr Pasternak’s team saw both sides swap 500 soldiers each in a two-day prisoner exchange.

But navigating these pockets of peace is not always smooth sailing.

“Usually, we’re responding by not bringing big bombs or heavy artillery to the area, but it can be another weapon, like small arms,” Mr Pasternak explained.

“On one occasion we came under mortar fire, but the Russian side saw this and called for it to be stopped.”

It is not uncommon for the Ukrainian negotiators in Mr Pasternak’s team to use the families of Russian prisoners of war to instigate talks.

“We’re connecting with chiefs of the Russian armed corps because relatives of Russian soldiers are sending messages to them that they have to interact with us,” Mr Pasternak said.

“And then these exchanges with the Russian militaries happen face-to-face at the front line, where we can also interact and talk about another exchange.”

But how does Mr Pasternak feel about maintaining positive relations with Russians to enable these exchanges?

“At every meeting I set, I tell my enemy that we are not friends,” he replied. “We are just doing our job. We are just here to return our people … end of story.”

In February, Volodymyr Zelensky revealed that some 7,000 Ukrainians were captive in Russia, while Ukraine held around 4,000 prisoners of war.

It is likely the numbers have increased significantly since the Ukrainian president gave his rare insight into the issue.

Dmytro Lubinets, Ukraine’s human rights ombudsman, said the soldiers had come home in poor health after the most recent prisoner exchange, having sustained injuries and been subjected to psychological distress.

But servicemen are not the only Ukrainians that Mr Pasternak and his team are attempting to bring back.

Kyiv claims that some 20,000 children have been forcibly removed from the country and illegally sent to Russia or Belarus.

“It’s very important for us to bring all of these kids back… Of course that is because the Russian authorities, the Russian military want to take these kids and make them Russian,” Mr Pasternak told The Telegraph.

But the process is not as easy as brokering man-for-man exchanges with the enemy.

In 2023, the International Criminal Court (ICC) issued arrest warrants for Vladimir Putin and Maria Lvova-Belova, his children’s rights tsar, for alleged war crimes involving Russia forcibly taking Ukrainian children.

Before the announcement, online Russian adoption databases were littered with adverts for Ukrainian children.

“They didn’t hide their faces, they didn’t hide where they were,” Mr Pasternak said. “But after the ICC brought forward its order, that all stopped.”

From that moment, it became harder for Ukraine to search for and identify kidnapped children being put up for adoption in Russia.

Earlier iterations of the peace proposals drawn up between US and Russian officials included exemptions for alleged war crimes committed during the course of the conflict.

Ukraine and its European allies have worked hard to remove this clause. Asked whether they had succeeded, Mr Pasternak replied: “I can’t give you the exact answer, but it depends on Russia.”