KYIV, Ukraine: Fighting has now begun inside Kostiantynivka, an important Ukrainian defensive city in the east that Russia has long sought to capture.

Ukrainian commanders said small groups of Russian soldiers are trying to enter the outskirts, which could lead to close-range battles soon.

At the same time, its progress along most of the 1,200-km front line has mostly stopped.

Kostiantynivka is the southernmost of four key towns that form a defensive line helping Ukraine protect the industrial Donetsk region.

Russia's push shows it still has more soldiers, even though Ukrainian drone attacks on supply lines have weakened its forces. Experts say these attacks have not been strong enough to stop Russia's offensive completely, and it can still attack in some areas despite heavy losses.

If Russia captures Kostiantynivka, it would gain a base from which to move farther north along this defense line. However, taking the city would likely be slow and very costly, similar to earlier battles in eastern cities like Pokrovsk and Avdiivka.

President Vladimir Putin has said Russia wants full control of Donetsk before the war ends. Ukraine still controls about one-fifth of the region after more than four years of fighting. Putin recently claimed Russia was close to taking the city, but Ukrainian commanders rejected this and said their troops are killing small groups of Russian soldiers entering the area.

A Ukrainian general said the city can still hold if current manpower and resources are maintained, though the situation is worsening. Analysts say Russia's advances are not enough for a quick breakthrough, but its gradual moves are making it harder and more costly for Ukraine to defend the city.

Some experts believe the fall of Kostiantynivka may only be a matter of time. Meanwhile, Russian forces are also advancing to the north of this defensive line and are threatening nearby cities like Sloviansk and Kramatorsk with frequent air and drone attacks.

Ukrainian supply routes are under heavy pressure, with constant shelling and bombing damaging roads and infrastructure leading north from Kostiantynivka, according to soldiers in the area.