Ukrainian service members fire a howitzer in Ukraine's Donetsk region on May 31.REUTERS/Viacheslav Ratynskyi Ukraine has switched up its tactics in its counteroffensive, reports say. Russia's extensive defenses along the front line have slowed Ukraine's progress. Ukraine has now turned to artillery fire, rather than pressing forward with tanks. Ukrainian ground forces have switched tactics in their counteroffensive to focus on artillery bombardment on Russian positions instead of attempting to push through with heavy armor, reports said.Ukraine's army has made slow and often costly gains pushing against Russian defensive lines using tanks and armored vehicles supplied by its allies.Ukrainian commanders told the Financial Times that there was increasing use of heavy artillery instead, intended to clear a path for sappers and infantry units.The report comes after Ukraine suffered considerable losses of Western-supplied heavy vehicles.However, according to the think tank the Institute for the Study of War, Ukrainian forces launched a significant mechanized counteroffensive operation in western Zaporizhia on July 26, and appear to have broken through some Russian defensive positions there.Two unnamed Pentagon officials told the New York Times that they believe these forces, which include infantry fighting vehicles and tanks, are the main attack of the counteroffensive underway since June, though others cautioned that they might be preparatory operations for the main thrust or perhaps just reinforcements to replenish war-weary units, the Times reported.It was on machines such as Bradley infantry-fighting vehicles, tanks, and mine-clearing equipment that Ukraine had pinned much of its hopes for its counteroffensive.