Explainer-Why is Russia trying to capture the Ukrainian town of Chasiv Yar?

By Andrew Osborn

LONDON (Reuters) - Russian paratroopers have reached the eastern edge of the Ukrainian town of Chasiv Yar, which Kyiv's top commander says Moscow wants taken by May 9, the date when Russia marks the Soviet victory over Nazi Germany.

The Kremlin has not acknowledged setting such a deadline, but Russian forces are pummelling the strategically-important Ukrainian town's defenders with artillery, drone and air strikes.

Colonel General Oleksandr Syrskyi, Ukraine's top commander, has warned that the battlefield situation in the east has deteriorated. But he has said that Kyiv's brigades in Chasiv Yar are holding back the assaults for now and have been reinforced with ammunition, drones and electronic warfare devices.

If Russian forces capture the town, 12 km (7.4 miles) from the centre of the devastated city of Bakhmut they took last May after months of bloody fighting, they would be able to launch direct offensives against several Ukrainian "fortress cities."

Moscow's forces, according to embedded Russian war correspondents and analysts, are likely to attempt to squeeze Ukrainian forces from the east, south and north in order to force them to flee westwards.

Russian soldiers have begun phoning their Ukrainian counterparts in Chasiv Yar to demand they surrender or be wiped out by guided aerial bombs, which Moscow's forces have used with devastating effect, according to Russian state news outlet Rossiyskaya Gazeta.

With warmer weather setting in, Kyiv, which is lobbying Washington to release a delayed aid package amid shortages of men and ammunition, fears Russia is preparing a major offensive across the more than 1,000 km-long (620-mile) frontline.

WHAT IS CHASIV YAR?

Chasiv Yar (Quiet Ravine), which had a pre-war population of more than 12,000 and is called Chasov Yar by Russians, sits in the industrial Donbas area in Ukraine's Donetsk region - one of four Ukrainian regions Moscow claims to have annexed.

Dissected by a canal, its pre-war economy centred on a factory that produced reinforced concrete products and mining fire (refractory) clay, which is resistant to high temperatures, and making products out of it such as bricks.

Located on higher ground, it has variously served as a regrouping point and as a forward artillery base for the Ukrainian army. It has been extensively shelled and damaged by Russian forces.

Ukraine says a Russian strike on residential buildings in the town in 2022 killed at least 43 people. Russia says those killed were Ukrainian troops.

Only a few hundred mostly elderly residents remain, some of whom are evacuating. Those that are still there shelter in basements and rely on volunteers for food and water.

The mayor of the town fled long ago, and Serhii Chaus, head of the local military administration, drives aid into the town from other centres.

WHAT'S AT STAKE?

Russian military analysts list Sloviansk, Kramatorsk, Druzhkivka, and Kostiantynivka as the "fortress cities" in Ukraine's east accessible from Chasiv Yar.

The Washington-based Institute for War Studies (IWS) think-tank describes the cities as "the backbone" of the Ukrainian army's defence in the east.

"The offensive effort to seize Chasiv Yar offers Russian forces the most immediate prospects for operationally significant advances," ISW said in a briefing note.

The ISW warned that losing Druzhkivka and Kostiantynivka in particular would be a major operational setback that would be hard to reverse.

WHAT SHAPE IS THE BATTLE LIKELY TO TAKE?

Casualties on both sides during Russia's lengthy capture of Bakhmut and Avdiivka, to the south, have been high, though no reliable public data exists on the scale.

Sergei Markov, a former Kremlin adviser, forecast the battle for Chasiv Yar would be equally hard from a Russian perspective.

"The 'fighting for Chasov Yar' period has begun. It will be long. The fighting will be about the same as for Bakhmut," Markov wrote on his official blog.

Alexander Kots, a war correspondent for Russia's Komsomolskaya Pravda newspaper who often travels with the Russian army, said airborne forces were trying to advance.

"To enter, it is necessary to first level the flanks and encircle the city, providing several entry points from different directions at once," Kots wrote on the Telegram messenger service.

"This is necessary in order to stretch the enemy's defence forces in the city and to force them to constantly move in different directions under our constant fire."

Ukrainian analysts with Deep State UA, a group that closely tracks the war, said on X that Russia was gathering reserves for the battle of Chasiv Yar.

(Reporting by Andrew Osborn; Editing by Philippa Fletcher)