For a 400-strong Ukrainian army unit based around the south-eastern village of Stepanivka, mid-August was the moment their lives turned to horror.
For a couple of weeks the unit had faced skirmishes with pro-Russian separatists. But the soldiers had fulfilled their task of preventing supplies flowing from across the nearby Russian border and along the road to the rebel stronghold of Donetsk, 100km northwest.
“Then the Russians invaded,” one soldier from the unit told the Financial Times, clutching his charred and swollen fingers.
Dozens of unmarked tanks, armoured personnel carriers, missile launchers and military trucks, he said, appeared on the road from the border. The unit suddenly faced not just the rebels but regular Russian troops, and artillery barrages from inside Russia that turned the area into what another survivor called a “furnace, pure hell”.
When rumours spread that Chechen mercenaries – with a reputation for torturing captives – would follow in a “clean-up” operation, what remained of the Ukrainian unit panicked.
“Some of our boys shot themselves in the head, right in front of me,” said the soldier, asking not to be identified as he was not authorised to speak to the press. “Others dropped their weapons and fled on foot, chased through the fields. A handful of us were lucky to get out alive.”
The entry of regular Russian soldiers turned the tide in the four-month-old conflict in east Ukraine, reversing the fortunes of Ukrainian forces that had seemed poised to rout the rebels.
It proved that Russian president Vladimir Putin was ready to do whatever was necessary to prevent a rebel defeat, and turned what had purported to be an internal Ukrainian conflict into an undeclared Russia-Ukraine war.
Petro Poroshenko was cornered into seeking a now week-old ceasefire and pursuing a deal with Mr Putin – even if that might leave rebels in control of parts of the east, giving Moscow leverage over Ukraine for years.
“We can’t win in a fight against Russia except in the way the Soviet Union did in the second world war – by slaughtering thousands of our citizens,” said one presidential adviser.
The outside world learnt of the extent of the Russian build-up inside Ukraine only on August 28, when Nato said “well over 1,000” Russian soldiers had been deployed there. By late last week, Nato put the number at 3,000; Ukrainian officials say the numbers might have topped 10,000.
Despite repeated denials from Moscow, Kiev officials and Ukrainian soldiers allege Russian special forces and military intelligence, in small numbers, have been directing the eastern insurgency since the start in April.
But the build-up of Russian regular forces, says Oleksandr Danylyuk, an adviser to Ukraine’s defence minister, began about a month ago. At the time a 280-truck Russian humanitarian aid convoy set off outside Moscow bound for eastern Ukraine, a mission Mr Danylyuk suggests was a decoy.
Russian military columns started moving across the border in several locations, quickly overwhelming Ukrainian border units such as that near Stepanivka.
Simultaneously, said a soldier from another Ukrainian border unit near Amvrosiivka, Russian artillery attacks from behind its border created a killing zone. “We were getting constantly shelled from Russian soil without the right to fire back,” says the soldier.
Ukrainian soldiers said separatist forces were ill-equipped and ill-disciplined. Russian forces, by contrast, were well organised, with much better weapons than the underfunded Kiev troops.
These included fearsome Uragan rockets, which can rain red-hot shrapnel in precision strikes from 35km away. “Our soldiers were getting wiped out and they never even saw the enemy,” the presidential adviser said. “It was like a meat grinder.”
Some Russian forces crossed the border near the other main rebel-held city of Lugansk, driving Ukrainian forces out of the city’s airport. Others launched a southern front, helping rebels seize the town of Novoazovsk on the Sea of Azov coast. That raised fears in Kiev that they could advance to the strategic port of Mariupol and open a land corridor west to Crimea, annexed by Russia in March.
Russian troops also moved towards Donetsk, retaking towns Ukrainian forces had seized just weeks earlier. Some Russian forces that smashed the Ukrainian units at Stepanivka and Amvrosiivka are believed to have ended up in Ilovaisk, 20 miles southeast of Donetsk, for a vicious and decisive battle.
After a pro-Kiev battalion seized part of the town in mid-August and pleaded for reinforcements, Mr Danylyuk said some 3,000 Ukrainian army troops were sent in support. They were quickly encircled and pounded by the newly arrived Russian forces.
When Ukrainian and volunteer soldiers negotiated with Russian commanders what they believed was a safe “corridor” out of Ilovaisk on August 29 and began to pull out, they were ambushed. More than 200 Ukrainians died in the carnage, taking the official number of pro-Kiev soldiers dead in the conflict to almost 1,000 – though many troops on the ground believe the true total is much higher.
“Ilovaisk was a catastrophe. It demoralised our military,” said another presidential adviser.
By September 1, rebels once again controlled Ilovaisk. In the early morning of September 3, Mr Poroshenko called Mr Putin to discuss a potential peace deal.