Ukrainian President Volodymyr Zelensky has vowed not to retreat from Bakhmut as Russian forces encroached on the devastated eastern city they have sought to capture for six months at the cost of thousands of lives.

Less than a week ago, an adviser to Mr Zelensky said the defenders might retreat from Bakhmut and fall back to nearby positions.

But Mr Zelensky on Monday chaired a meeting in which top military brass “spoke in favour of continuing the defence operation and further strengthening our positions in Bakhmut”, his office said.

Later, in his nightly video address, the president said his advisers unanimously agreed to press on with the fight, “not to retreat” and to bolster Ukrainian defences.

Mr Zelensky’s top adviser, Mykhailo Podolyak, said no decision has been made to retreat because of “a consensus among the military about the need to continue defending the city” and grinding down enemy forces “while building new lines of defence”.

By pressing the defence, Ukraine has exhausted Russia’s main combat-ready groups and trained tens of thousands of Ukrainian military personnel for a possible counteroffensive, he said.

Intense Russian shelling targeted the city in the Donetsk region and nearby villages as Moscow waged a three-sided assault to try to finish off Bakhmut’s resistance.

The nearby towns of Chasiv Yar and Kostiantynivka came under heavy shelling, damaging cars and homes and sparking a fire. No casualties were immediately reported.

Police and volunteers evacuated people from Chasiv Yar and other frontline towns in an operation made difficult by the loss of bridges and constant artillery fire which has left barely a house standing.

Russian forces have been unable to deliver a knockout blow that would allow them to seize Bakhmut. Analysts say it does not hold major strategic value and its capture would be unlikely to serve as a turning point in the conflict.

The Russian push for Bakhmut reflects the Kremlin’s broader struggle to achieve battlefield momentum. Moscow’s full-scale invasion on February 24 2022 soon stalled and Ukraine launched a largely successful counteroffensive.

Over the bitterly cold winter months, the fighting has largely been deadlocked.

The city’s importance has become mostly symbolic. For Russian President Vladimir Putin, prevailing there would finally deliver some good news from the front. For Kyiv, the display of grit and defiance reinforces a message that Ukraine is holding on after a year of brutal attacks, justifying continued support from its western allies.

US secretary of defence Lloyd Austin endorsed that view on Monday, saying during a visit to Jordan that Bakhmut has “more of a symbolic value than … strategic and operational value”.

Moscow, he added, continues “to pour in a lot of ill-trained and ill-equipped troops” into Bakhmut, while Ukraine patiently builds “combat power” elsewhere with western military support ahead of a possible spring offensive.

Even so, some analysts question the wisdom of ordering Ukrainian defenders to hold out much longer. Others suggest a tactical withdrawal may already be underway.

Michael Kofman, the director of Russia studies at the Can think tank in Arlington, Virginia, said Ukraine’s defence of Bakhmut has been effective because it has drained the Russian war effort, but that Kyiv should now look ahead.

“The tenacious defence of Bakhmut achieved a great deal, expending Russian manpower and ammunition,” Mr Kofman tweeted late on Sunday. “But strategies can reach points of diminishing returns, and given Ukraine is trying to husband resources for an offensive, it could impede the success of a more important operation.”

The Institute for the Study of War (ISW), a Washington-based think tank, said Kyiv’s smartest option now may be to withdraw to positions that are easier to defend.

“Ukrainian forces are unlikely to withdraw from Bakhmut all at once and may pursue a gradual fighting withdrawal to exhaust Russian forces through continued urban warfare,” the ISW said in an assessment published late on Sunday.

The Bakhmut battle has exposed Russian military shortcomings and bitter divisions.

Yevgeny Prigozhin, the millionaire owner of the Wagner Group military company which has spearheaded the Bakhmut offensive, has been at loggerheads with the Russian defence ministry and repeatedly accused it of failing to provide his forces with ammunition.

On Sunday, he again criticised top military brass for moving slowly to deliver the promised ammunition and questioned whether the delay was caused “by red tape or treason”.

On Monday, Mr Prigozhin said in a Russian social media post that the situation in Bakhmut “will turn out to be a ‘pie’: The filling is the parts of the Armed Forces of Ukraine surrounded by us (in the case, of course, if there is a complete encirclement of Bakhmut), and the shell is, in fact, the Wagner” Group.

Bakhmut has taken on almost mythic importance. It has become like Mariupol — the port city in the same province that Russia captured last year after an 82-day siege which eventually came down to a mammoth steel mill where determined Ukrainian fighters held out along with civilians.

Moscow looked to cement its rule in Mariupol. Russian defence minister Sergei Shoigu toured some of the city’s rebuilt infrastructure — a newly built hospital, a rescue centre and residential buildings — the defence ministry said.

In other developments on Monday:

— Russian forces attacked central and eastern regions of Ukraine with Iranian-made Shahed drones, said a spokesman for Ukraine’s Air Forces, Yurii Ihnat. Of 15 drones Russia launched, 13 were shot down, Mr Ihnat said. It was not immediately clear if the attack caused damage.

— Russian defenders shot down three missiles over Russia’s Belgorod region on the border with Ukraine, its governor, Vyacheslav Gladkov, said on Telegram. Debris injured one person and damaged power lines and facades of residential buildings, according to the official. Mr Gladkov did not specify whether the missiles were fired from Ukraine.

— Ukraine’s chief prosecutor announced a criminal investigation into what appeared to be Russian troops’ execution of an unarmed Ukrainian prisoner of war. A video circulating on social media showed a uniformed Ukrainian soldier standing and smoking. The soldier says “Glory to Ukraine” before a volley of gunshots hits him and he falls into a shallow hole dug into the ground. The Associated Press could not verify the authenticity of the video.

— Russia’s Federal Security Service (FSB) reported thwarting an attempt to assassinate nationalist businessman Konstantin Malofeyev which was allegedly plotted by Ukrainian security services and the Russian Volunteer Corps which claims to be part of Ukraine’s armed forces. According to the FSB, the Russian Volunteer Corps leader Denis Kapustin was the mastermind behind the plan, which was to put a bomb under Mr Malofeyev’s car.

Mr Malofeyev is a media baron and owner of the ultra-conservative Tsargrad TV who has supported Russia-backed separatists in Ukraine and trumpeted Moscow’s invasion as a “holy war”. He has been sanctioned by the US and last year was charged with trying to evade sanctions.

The Russian Volunteer Corps last week claimed responsibility for an attack on Russian villages on the border with Ukraine. The FSB said on Monday Mr Kapustin organised and spearheaded the raid, which killed two civilians and wounded two others. The FSB’s allegations could not be independently verified. Ukrainian officials have not commented.