KYIV, Ukraine (AP) — The Zaporizhzhia region of southeast Ukraine has become the most recent hot spot for battles in the 18-month war, Russian Defense Minister Sergei Shoigu said Tuesday, as Kyiv’s forces press ahead with their counteroffensive.

Shoigu told Russian military officers that Ukraine has brought up reserve brigades there that were trained by Kyiv’s Western allies. He offered no evidence for his claim, which could not be independently verified.

Fighting in the southeast could be one of the keys to the war. If Russian defenses there collapse, Ukrainian forces could push southward toward the coast and potentially split Russian forces into two.

Shoigu’s assertion was corroborated in part by other reports and assessments of Ukraine’s three-month-old effort to drive out the Kremlin’s troops.

The Institute for the Study of War, a think tank, citing geolocated footage, said Tuesday that Ukrainian light infantry has advanced beyond some of the anti-tank ditches and dense minefields that make up Russia’s layered defenses in Zaporizhzhia.

However, it said it was unable to state that the defense was fully breached, because no Ukrainian heavy armor has been witnessed in the area.

It is in the south that the Ukrainian brigades have made most recent battlefield gains as the counteroffensive inches forward under heavy fire.

Since the grinding counteroffensive began about three months ago, Ukraine has advanced 7 kilometers (4.3 miles) in the Zaporizhzhia region, Ukrainian officials claim. Troops surmounted dense Russian fortifications last week to retake the village of Robotyne. That was Ukraine’s first tactically significant victory in that part of the country.

Ukrainian forces have made more progress in that area and were fortifying captured positions on Tuesday morning, according to Pavlo Kovalchuk, spokesman of the General Staff of the Armed Forces of Ukraine.

Neither side’s battlefield claims could be verified.

If Ukrainians progress just 15 kilometers (9 miles) from Robotyne, they could come within firing range of Russia’s east-west transport routes and potentially weaken Moscow’s combat capabilities, military observers say.

Ukrainian forces are advancing without air cover, making their progress harder and slower, while Russia has launched its own push in the northeast to pin down Ukrainian forces and prevent them being redeployed to the south.

Ukraine has adapted its counteroffensive tactics in recent weeks, moving from attempts to bludgeon its way through Russian lines using Western-supplied armor to better-planned tactical attacks that make incremental gains, according to the Royal United Services Institute, a think tank.

“However, this approach is slow, with approximately 700–1,200 meters (2,300-4,000 feet) of progress every five days, allowing Russian forces to reset,” it said in an assessment Monday.

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