Russian authorities struggled on Tuesday to extinguish a massive fire in the southern Rostov region for the third consecutive day after a Ukrainian drone struck an oil depot, while Kyiv's forces also advanced into the Russian Kursk region.

The fire broke out at the depot in the town of Proletarsk across an area of a hectare (2.5 acres), according to official Russian news agencies. There are 500 firefighters participating in the operation, with 41 of them already hospitalized due to injuries, according to state-owned Russian news agency TASS, citing local officials.

For its part, the Ukrainian General Staff announced on Sunday its responsibility for attacking the oil depot, which was used to supply the Russian army, describing it as a measure "to undermine the military and economic potential of the Russian Federation."

Meanwhile, hundreds of kilometers northwest, Ukraine continued its operations in the Russian Kursk region.

Ukrainian President Volodymyr Zelensky said that the bold incursion into Kursk allowed his army to capture a large number of Russian prisoners who could be used in exchange for the release of Ukrainian captives, thereby expanding Kyiv's objectives for the mission launched two weeks ago. He previously explained that Ukraine aims to establish a buffer zone that may prevent further cross-border attacks by Moscow, especially with long-range artillery, missiles, and glide bombs.

Zelensky told diplomats on Monday, according to a statement posted on Telegram late in the day: "Overall, this operation (Kursk) has become our largest investment in the process of liberating Ukrainian men and women from Russian captivity." "We have already captured the largest number of Russian prisoners in a single operation."

Zelensky stated that the Ukrainian army seized 1,250 square kilometers (480 square miles) and 92 settlements in the Russian Kursk region.

The Institute for the Study of War, a Washington-based research center, reported that Ukrainian forces "continued to make slight advances" in Kursk on Monday.

The invasion of Ukraine, the largest assault on Russia since World War II, has revealed Russian weaknesses under the leadership of President Vladimir Putin.

Zelensky stated: "Our defensive actions across the border, as well as Putin's inability to defend his territory, have clear implications. Our proactive defense is the most effective means to counter Russian terrorism, causing significant difficulties for the aggressor."

TASS reported that 17 people have died and 140 others have been injured in the Ukraine invasion, citing an unnamed source in the Russian medical service. Among the 75 people hospitalized, four are children.

Ukrainian and Russian reports indicate that Ukraine has destroyed or damaged at least three bridges over the Sim River in the Kursk region - a move that could trap Russian forces between the river and the Ukrainian advance and border.

Over the weekend, the commander of the Ukrainian Air Force posted two videos of bridges over the Sim River being bombed, and satellite images captured by Planet Labs PBC and analyzed by the Associated Press on Tuesday confirmed that a bridge in the town of Glushkovo has been clearly destroyed. There was visible satellite evidence of mechanical maneuvers by forces in the Kursk region, but no clear image of the fate of the remaining two bridges.

A Russian military investigator confirmed on Monday that Ukraine "completely destroyed" one bridge and damaged two others in the area.

An unnamed representative for the Russian Investigative Committee stated in a video posted on the Telegram channel of Russian government broadcaster Vladimir Solovyov: "As a result of targeted shelling using rocket and artillery weapons against residential buildings and civilian infrastructure in the village of Karizh... a third bridge over the Sim River has been damaged."

The floating bridges - temporary bridges used by armies when official bridges are blown up - can be seen in satellite images at two different locations along the Sim River in recent days. The floating bridges likely have been built by Russian forces attempting to supply troops around the Ukrainian advance.

A floating bridge appeared along the winding course of the river between Glushkovo and the village of Zvanovoye on Saturday, but not in images captured on Monday. Smoke could be seen rising along the nearby riverbanks - usually a sign of an attack.

However, even with Zelensky praising the successes in Kursk, his forces face a grim situation in the Donbas region of eastern Ukraine, where they are fighting Russia. The Russian assault on the city of Pokrovsk forces Kyiv's troops to withdraw and Ukrainian civilians to flee their homes.

The ongoing Russian push over the past six months through the Ukrainian Donetsk region after capturing Avdiivka has cost both sides heavy casualties in troops and armor.

Russian forces are heading towards Pokrovsk, one of Ukraine's main defensive strongholds and a key logistics hub in the Donetsk region. Capturing it would jeopardize Ukraine's defensive capabilities and supply routes, bringing Russia closer to its stated goal of seizing the entire Donetsk region.

Russia seeks to control all parts of Donetsk and neighboring Luhansk, which together make up the industrial Donbas region.