Trenches with basic living quarters are being dug here under cover of darkness. Artillery rumbles can be heard nearby.

These are the country's new northeastern defensive lines.

A Reuters visit on December 28 showed how the country has stepped up construction of its fortification in recent months.

It's part of a shift in military operations against Russia to a more defensive footing.

The goal? To help Ukraine weather assaults while regenerating its forces, as Moscow takes the battlefield initiative, according to military analysts.

Reuters spoke to a Ukrainian army engineer, whose call sign is "Lynx".

"As soon as the troops are moving, traversing fields, you can do without fortifications. But when the troops stop, you need to immediately dig in. This guarantees us safety."

The lines bear some similarities to those rolled out in the Russian-occupied south and east.

Lynx says Ukraine is trying to minimize the use of mines for its fortifications to avoid leaving dangerous munitions on its territory.

"This is our land," he says, "We wouldn't want to litter it so much".

President Volodymyr Zelenskiy announced that Ukraine was "significantly enhancing" its fortifications in late November.

That's after a slow progressing counteroffensive it launched in June.

"The main task for us engineers is to ensure the mobility of our troops and to make it as difficult as possible for the enemy's troops to move. We do all types of barriers, whether mined or without mines. Our job is all about fortified areas."

Kyiv says its ambition is still to recapture all occupied territory.

But its current focuses are politically sensitive conscription reforms to help replenish its manpower, and artillery shortages at the front.

Analysts say that Russia has been ramping up offensive pressure around eastern towns.

And that it no longer needs to hold back its reserve troops for fear of a possible Ukrainian breakthrough.

Jack Watling of the Royal United Services Institute said stronger fortifications would slow down Russian troops and suck fewer Ukrainian forces into defense, potentially freeing them up from the front for more training.

And they could also be used to defend Ukraine's flanks when it goes back on the offensive.

Ukrainian joint forces commander Serhiy Nayev says the military has expanded its defensive fortifications in the north by 63% in the last few months.

Zelenskiy said Ukraine's defensive constructions needed to be boosted and accelerated in regions stretching all the way up from Ukraine's east, along the border with Russia and Belarus, to its western ally Poland.