In the lead-up to Monday’s attack, Russian forces were regrouping in the east after failing to capture a single major Ukrainian city when it began a widespread invasion on Feb. 24.
Now, both sides say the war has entered a new phase in a region that has been plagued by conflict for eight years between Russian-backed separatists and Ukrainian forces.
Here’s what you need to know:
Where is Donbas, and what has happened so far?
The Donbas region, which consists of Donetsk and Luhansk provinces, is located in eastern Ukraine near the Russian border.
Russian forces are now attacking Donbas with troops approaching from several directions, according to an intelligence briefing published by Britain’s defence ministry on Tuesday.
In the first reported success of Russia’s new assault, Ukraine said the Russians had seized Kreminna, a front line town of 18,000 people in Luhansk, one of the two Donbas provinces.
Ukrainian media reported explosions along the front lines in the Donetsk region overnight, with shelling taking place in nearby Marinka, Sloviansk and Kramatorsk.
Ukraine’s top security official, Oleksiy Danilov, said Russian forces have attempted to break through Ukrainian defences “along almost the entire front line of Donetsk, Luhansk and Kharkiv regions.”
However, Ukrainian officials insist their troops can withstand the new assault, and that Russian forces will fail in achieving their objectives.
Why is the Donbas region significant, and why is Russia focused on it?
Just before the full-scale war began, Russian President Vladimir Putin recognized the cities of Donetsk and Luhansk in Donbas as independent states, home to two Russian separatist movements since 2014. Putin’s Feb. 21 decision drew widespread criticism from the West, which recognizes the regions as Ukrainian territory.
The Donbas region is home to a majority of Ukraine’s Russian speaking population, and Moscow wants the “liberation” of the region as part of its “special military operation” that has left a trail of destruction across Ukraine.
A few weeks ago, Russia announced it would reduce its operations around the capital Kyiv in what the head of the NATO military alliance called a regrouping for the new offensive.
“In the coming weeks, we expect a further Russian push in eastern and southern Ukraine to try to take the entire Donbas and to create a land bridge to occupied Crimea,” said Secretary-General Jens Stoltenberg on April 5.
The coal and steel producing Donbas region has been the focal point of Russia’s campaign to destabilize Ukraine since 2014, when the Kremlin used proxies to set up separatist “people’s republics” in parts of the Luhansk and Donetsk provinces.
Now, Moscow said its aim is to capture the full provinces on behalf of the separatists. Ukraine has a large force defending the northern section of Donbas, and military experts say Russia probably aims to cut the Ukrainians off or surround them.
Part of the greater Donbas region is the besieged city of Mariupol, which is near occupied Crimea, said Andrew Rasiulis, a defence expert with the Canadian Global Affairs Institute.
Russia annexed Crimea in 2014, and by controlling Mariupol and Donbas, it could result in the uninterrupted flow of goods for example, and would be a much-needed victory for the Russians, Rasiulis said.
“So with this objective, the Russians will consolidate their position in Crimea. They will also consolidate their position in the coal-mining region of the Donbas, which is historically the Russian speaking area of Ukraine,” he told Global News.
“Having done that, they can declare a military victory, which they translate into a political victory, and a political victory is much more modest. It’s no longer all of Ukraine as a buffer … it’s the Donbas as a buffer.”
How could the Donbas region change the outcome of the war?
It’s unclear what would happen if either side were to declare victory in Donbas, but Rasiulis said prolonged fighting could potentially lead to a ceasefire between Ukraine and Russia.
“This might happen here because politically, it’s hard now to see a settlement between the Ukrainians and the Russians,” he said.
“There’s been so much animosity shed, and there’s been so much destruction now that a ceasefire, an armistice, basically they just agreed to stop killing each other and neither one accepts the other’s position.”
Russia desperately needs a win after its failed attempt to occupy Kyiv and overthrow the government, said Ret. Canadian Maj. Gen. Denis Thompson.
With that in mind, the conflict in the Donbas region could bring the war into a “long slugfest” with little territory gained, he said.
“It’s worth noting that many of the (Russian) troops that they’re going to use are coming from a failed effort in Kyiv … their morale was poor when they went into the area around Kyiv … and I don’t imagine that their morale is any better,” said Thompson, a former commander of NATO’s Task Force Kandahar.
“The Russians will revert to their norm, which is to pound away using artillery, rockets and air power to the extent that they can because they still haven’t imposed air dominance over the region, and they will try and blast their way through while the Ukrainians will stay in dispersed formations and … wear their morale down in a similar fashion as they did around Kyiv.”
How could the West respond in the meantime?
Canada and its allies met on Tuesday in response to the new offensive. To date, the allies have levied unprecedented sanctions against Russia and its supporters in an effort to cripple Moscow’s ability to wage war.
Ottawa on Tuesday announced it was sanctioning 14 “close associates” of the Russian regime, including Putin’s two adult daughters.
The allies have refused to deploy troops to Ukraine, or enforce a no-fly zone in fears it will lead to an escalation that will draw more nations into war. However, they have upped shipments of lethal and non-lethal aid to Ukraine to help in its defence.
The West must double down on its support for Ukraine going forward, said Rasiulis.
“The West is going to do everything it can to support the Ukrainians, short of actual combat. Then the question is, will the Russians be able to overcome this?” he said.
“There’s a possibility the Russians may succeed in this; they have numbers on their side, and they have some time on their side in this limited operation there. They have those short lines of communication directly from Russia, so they can keep pounding away.”
NATO has promised to up its weapons shipments to Ukraine in light of the Donbas offensive, but Thompson said it must include weapons the Ukrainians have been trained to use, like the U.S. Javelin missile for example.
“All of this is going to bolster Ukraine and give them the ammunition they need to fight back,” he said.
“It’s not a question of will – they certainly have that – it’s a question of whether they have the material resources to push back the Russians, and so we need to continue to provide those lethal assets.”
— with files from Reuters