Why is the war in Ukraine suddenly going from frozen conflict to scorcher? Is this Vladimir Putin’s way of testing Donald Trump, not two full weeks into his job as U.S. president, or is it just another provocation designed to keep Kiev weak and insecure after three years of invasion, annexation and occupation?

True, fighting has continued more or less constantly in east Ukraine, the industrial heartland known as the Donbass, ever since the fighting was meant to have stopped as a result of not one but two cease-fire agreements. But this week it escalated in a dramatic fashion, and with clear signs of Kremlin support. Into the fray on the pro-Russian separatists’ side have come heavy-duty armaments such as Grad rockets and the Buk missile system which shot down MH17. (And there’s only one place where the separatists can get this stuff). Also, Ukrainian soldiers are receiving ominous text messages on their cell phones, redolent of the kind of cyber-ops used against them before in the war, the technology and operators of which have been linked to Russian military intelligence hacking of the DNC and Hillary Clinton’s emails.

According to Ukrainian official reports, at least 12 Ukrainian soldiers have been killed and 57 wounded since Sunday, along with civilian killed and five wounded. The Russia-backed separatists in Donetsk report at least nine of their fighters and five civilians dead, though it must always be cautioned that the so-called Donetsk People’s Republic has form for exaggerating or even outright fabricating reports of civilian casualties. Nevertheless the fighting is the worst seen in an urban area in well over a year.

Avdiivka is of key economic importance to the Donetsk region, housing the vast Avdiivka coke and Chemical Plant, the biggest coke producer in Ukraine and one of the largest in Europe. The plant forms a key part of the metallurgy industry in the Donbass, the backbone of the region’s economy, providing coke for steel works in Mariupol, another government-held city threatened by Russia-backed forces down on the Azov coast.

Since the fall of Donetsk Airport to Russia-backed forces in January, 2015, Avdiivka has borne the brunt of fighting in the Donetsk area, and has been the scene of daily attacks since. Violence has remained at a relatively high level since March last year, when Ukrainian troops established control over the Avdiivka industrial park or promzona, which had formally laid in no-man’s land since the signing of the second Minsk peace agreements in February, 2015, bringing them to within a few hundred meters of Russia-backed forces’ positions on the highway out of Donetsk city.

The battle around Avdiivka began in the early hours of Sunday morning and there are two competing narratives of what happened.

According to the Ukrainian military, Russia-backed fighters launched a series of assaults on Ukrainian positions both in the promzona, and to the southwest and east of the town. In response, say reports from both front-line fighters and the Ukrainian defense minister, Stepan Poltorak, Ukrainian forces mounted a successful counter-attack and took over some of the Russia-backed fighters’ foremost trenches. Meanwhile, the separatists and their handlers in Moscow claim that the battle was initiated by a Ukrainian offensive.

Since then, fighting has intensified across the front line, well beyond Donetsk, with heavy shelling reported every day from Mariupol to the Luhansk region in the northeast.

Devastating and highly inaccurate Grad multiple-launch rocket systems are now back in regular use. Video from Donetsk city on Tuesday morning showed repeated volleys of the 122-mm rockets flying out of separatist-held territory towards Ukrainian lines. There are also numerous reports of the use of such rockets both to the south of Donetsk and the east of Mariupol. While the Ukrainian military has reported the sporadic use of Grads on several occasions in the last year, this is the first significant use of the weapons in urban Donetsk since the summer of 2015.

With artillery raining down on both sides of the front line, residents of Donetsk and Avdiivka have been comparing recent days to the darkest days of the war at the height of fighting in 2014 and 2015.

One particularly disturbing development has been the dissemination of threatening SMS text messages in Avdiivka, addressed to Ukrainian soldiers, warning them that their bodies “will be found when the snow melts,” or that they are nothing but “meat for their commanders.” The appearance of such messages closely resemble those sent out en-masse during the bloody battle for Debaltseve in January and February, 2015, which ended in the fall of the city to the Russian army. These texts appear to have been broadcast by Russian electronic warfare systems, which have been documented in Donetsk within the last year, with the aim of demoralizing Ukrainian troops.

Another is the return of the Buk surface-to-air missile system, with which Malaysia Airlines flight MH17 was shot down on July 17, 2014. The separatists published images today showing the wreckage of what they claimed was the wreckage of a Buk missile that had crashed, without detonating, in the Donetsk suburb of Makiivka, allegedly having been fired by Ukrainian forces at a drone operated by the Organization for Security and Cooperation in Europe (OSCE) which is monitoring the conflict with the aim of securing a ceasefire. While the photos do appear to be genuine, the OSCE has explicitly denied that any of their unmanned aerial vehicles came under attack. There are also some reports from locals that the missile was fired from separatist-held territory.

The humanitarian situation in Avdiivka is grim. Shelling has knocked out power supplies, and civilians have been left without running water, heat or light as temperatures reach -17 Celsius during the nights. The authorities have established field kitchens and warming centers, but announced that they are prepared to evacuate thousands of residents, though as of Wednesday, only 145, 88 of them children, have chosen to leave.

What we have seen this week is a major deterioration. While the level of violence in Ukraine has ebbed and flowed on a relatively cyclical, though still deadly basis over the last year, there have been occasional flare-ups, most notably in December last year, when heavy fighting broke out and lasted for several days near Debaltseve, leaving dozens of fighters on both sides dead. However, this week’s combat differs significantly from December’s. Firstly, the worst fighting is taking place in built-up, urban areas, posing a far greater risk to civilians than the battles in the countryside outside Debaltseve. Secondly, the increase in shelling, including the use of Grads, elsewhere on the front line is far more dramatic and widespread last year.

This escalation comes as Ukraine is trying to shore up international support at a time of great uncertainty following the inauguration of President Donald Trump, whose relationship with the Kremlin has Kiev worried. Ukrainian President Poroshenko was in Berlin on Monday for talks with Chancellor Angela Merkel but cut his visit short due to the fighting. Meanwhile, both Danish and French ministers have been visiting Mariupol this week. A video released on Tuesday by the Danish foreign minister, Anders Samuelsen, captures the sound of distant shelling as the minister expressed his concern about the deterioration.

Many observers have noted that the explosion of violence came shortly after a phone call between Trump and President Vladimir Putin on Saturday, which, the Kremlin claims led to the two leaders agreeing to “establish partner-like cooperation” on the “crisis” in Ukraine—something the White House did not mention.

Could the Russians have launched an assault on Avdiivka having either felt they had received assurances from the White House that the US would not react, or to test the resolve of the new leader? Perhaps, but the relationship is likely more organic.

An important factor is that, over the last year, the Ukrainian armed forces have become significantly more assertive and effective in prosecuting counter-attacks, and bolder in establishing control over hirtherto-undefended areas, such as Avdiivka’s promzona or the villages of Novoluhanske [] near separatist-held Horlivka, and Vodyanoye, east of Mariupol.

While such moves by the Ukrainian military do not constitute violations of the Minsk agreements as the areas involved were already designated as being on the government-controlled side of the demarcation line, and have helped the army secure vulnerable territory and combat issues such as smuggling (which has become a deadly, multi-million-dollar industry), they do provide certain opportunities for Russia and the separatists.

Chiefly, the Russia-backed forces, having lost ground to counter-attacks near both Debaltseve and Avdiivka, can claim that Ukrainian forces are on the offensive, and justify their own attacks as retaliatory - a claim put forth this week by the Kremlin. Dmitry Peskov, Putin’s press secretary, told reporters on Tuesday that Ukraine’s actions in Avdiivka were “nothing other than a provocation,” claiming that “Donbass militiamen” had “been forced to respond” to a Ukrainian assault.

But it is the actions of Russia-backed forces themselves that appear to be provocations, as their fighters conduct assaults without the necessary force to actually break through Ukrainian lines and Russian-supplied rockets and shells rain down to little apparent military effect bar the infliction of casualties.

This is because the Kremlin has little to gain right now from an all-out assault as the sea change in Western politics, with the election of Trump and the strong possibility of a friendly government in France after the presidential elections later this year, means that the relief of sanctions is a growing possibility.

Instead, sensing that the U.S. and European Union are unlikely to impose additional sanctions this year, the Kremlin can pursue the path most likely to undermine the fragile stability of the Ukrainian government by increasing the rate of attrition in the Donbass and creating the impression of an impending offensive.

To boot, Ukrainian forces could be goaded into overreacting, allowing Moscow to claim that Kiev is abandoning the Minsk peace plan or even raising the possibility of an open intervention by Russian armed forces under the guise of peacekeeping.

Indicative of this is the emphasis given by Russian media to alleged attacks by Ukrainian forces on Russian journalists in Donetsk. On Sunday a crew from NTV filmed what they described as a shelling attack, marked by a chorus of shrieking babushki and the curious absence of any visual evidence of an attack. Then, on Tuesday, two groups of Russian journalists reportedly came under fire. A cameraman from LifeNews, a channel suspected of having close ties to Russia’s security services, was, the network said, injured after a Ukrainian shell exploded nearby.

Finally, today has seen what could be called a double provocation, this time in the Black Sea, after the Ukrainian defense minister reported that a Ukrainian military transport had been shot at by Russian sailors while flying over Ukrainian territorial waters. Despite photographic evidence that the plane had been struck by small-arms fire, the Russian military denied any such incident had taken place, instead accusing the Ukrainian aircrew of flying dangerously close to two drilling rigs and a Russian naval vessel. That the rigs were illegally seized by Russia during the annexation of Crimea and were operating in waters internationally recognized as being within Ukraine’s exclusive economic maritime zone did not prevent the Russian government from going further, by summoning the military attaché to the Ukrainian embassy in Moscow tonight to answer for the Ukrainian crew’s “clear provocation.”

Russia is playing a long game in Ukraine and the deadly violence around Avdiivka is just part of what looks likely to be a significant increase in pressure over the coming months as the Kremlin tries to do as much damage as possible while there is little probability of any real response from the West.