Ukraine retreats from pivotal eastern city Severodonetsk, a significant victory for Russia in its grinding advance

• Russia secured a victory as Ukrainian forces abandoned a major city on Friday.
• Russia fought for two months to seize the key city of Severodonetsk in the eastern Donbas region.

Russia secured a major victory on Friday as Ukrainian troops were ordered to abandon a key city in the Donbas region.

Ukrainians defending Severodonetsk in the Donbas region were ordered to pull out to avoid being encircled by Russian troop who had been gradually advancing.

"It makes no sense to remain on positions that have been demolished," Serhiy Haidai, governor of the Luhansk Oblast, in which Severodonetsk is located, told Ukrainian TV on Friday.

"The defenders have already received orders to pull back to new positions, new fortified areas, and to conduct full military activities and to inflict damage on the enemy from there."

Haidai was putting a brave face on a development that marked another gain for Russia in its steady, grinding advance through eastern Ukraine.

After failing to seize the capital Kyiv earlier this year, President Vladimir Putin focussed all his attacks on the Donbas, much of has been was controlled by pro-Kremlin separatists since 2014.

The battle for Severodonetsk lasted more than two months and it loss is a major blow for Ukraine.

Russia has in recent weeks started to notch up a series of small wins in its efforts to expand its front line in the Donbas.

However, the conflict has slowed in recent weeks, with each side digging in and preparing for a long, attritional war.

Two US officials told CNN that Russia is starting to eliminate the errors that plagued its early invasion, for example by better coordinating air and ground attacks and improving logistics and supply lines.

In turn, Ukraine's defensive efforts were bolstered this week by the arrival of HIMARS long-range rocket systems from the US — a tool Ukraine has long said it key to fighting back against Russia.