KIEV — Ukrainian forces are expanding their cross-border advance into a new Russian border region as Moscow sends reinforcements to the area to repel the biggest attack on Russian soil since the war began.

Ukraine has also reportedly captured a key strategic target that could be useful to Kyiv in future peace talks with Moscow: a major gas pipeline hub. At the same time, Russia is desperately trying to defend a nearby nuclear power plant that could also be in Ukraine’s sights.

Ukrainian armed forces released a video on Saturday from the Russian village of Poroz in the Belgorod region in which their soldiers are holding a Ukrainian flag.

Meanwhile, Russia has declared an “anti-terrorist operation” in three regions – Kursk, Belgorod and Bryansk – as Ukrainian troops advance. The Russian protocol includes vehicle checks, monitoring of phone calls and tighter security measures.

Previously, the Russian government imposed similar measures during the short-lived Wagner Group uprising in Moscow in June 2023.

The Russian Defense Ministry said it had sent weapons and equipment to Kursk to bolster support after the government declared a federal state of emergency in the region. Videos published by the Russian press showed columns of military trucks carrying artillery guns and tanks.

An air raid warning was sounded overnight in the Ukrainian region of Sumy, which borders Kursk Oblast, and Ukrainian authorities began evacuating about 20,000 people from the area on Friday.

The General Staff of the Ukrainian Armed Forces confirmed on Friday that they had attacked a military airport in the Russian region of Lipetsk. The target was an ammunition depot containing missiles. Videos published by local media and residents showed that a major fire broke out as a result of the explosion.

The Russian government evacuated people living near the air base after Ukraine’s “massive attack” caused explosions, a power outage and nine injuries, regional governor Igor Artamonov said via Telegram.

Videos are being released as a sign that Ukrainian forces intend to hold the captured territory shows Signs of Russian cities now have the Ukrainian spelling and a Ukrainian flag appears under the names.

A video shows soldiers of the 61st Brigade Speaking of at the Gazprom offices in Sudzha in the Kursk region. “The city is under the control of the Ukrainian armed forces and it is quiet,” the Ukrainian soldiers said.

The capture of Sudzha could represent a strategic advantage for Kyiv, as it is home to two important Russian gas pipelines that transport energy supplies from Siberia and the Arctic to the West.

Control of the gas pipeline hub – a “strategic prize”, as the Sun’s James Brooke reported – could be used as a “bargaining chip” in potential ceasefire talks between Russia and Ukraine.

Meduza, an independent Russian news website based in Latvia, reports that Ukrainian forces have captured the “gas metering station” in Sudzha, which is “the last remaining Russian pipeline that still carries gas through Ukraine to Europe.” However, Meduza says gas is still flowing through the pipeline.

Local press reported on Saturday that Russian troops were deployed to defend the Kursk nuclear power plant – another potential strategic target for Kyiv – as Ukrainian forces expand their attacks further into Russia. The plant is located in the town of Kurchatov, 79 kilometers from Ukrainian-occupied Sudzha.

The International Atomic Energy Agency (IAEA) has expressed concern about military activities near the power plant. IAEA President Rafael Mariano Grossi released a statement reminding both the Russian and Ukrainian governments of the protocols for ensuring nuclear safety during an armed conflict.

“I would like to call on all sides to exercise maximum restraint to avoid a nuclear accident with potentially serious radiological consequences,” Grossi said in a statement. “I am personally in contact with the relevant authorities in both countries and will continue to monitor the matter.”

The Ukrainian government has not released any information about the operation in the Kursk region.

A senior adviser to Ukrainian President Selensky, Mykhailo Podoliak, said Social media reports say that a significant portion of the international community now views Russia as a target for operations.

“The impossible has become possible, and the mythical ‘Russian brutality and limitlessness’ has turned against Russia itself,” Podolyak wrote.

Analyst Emil Kastehelmi of the Finland-based Black Bird Group, which analyzes military movements related to Russia’s war in Ukraine, wrote that the invading Ukrainian units had successfully exploited the disorganization of the Russian defense – at least for now.

“Time is also running out for the Ukrainians. Russia will not remain disorganized forever,” warns Kastehelmi. “At least in the information sector, the Russians are suffering an embarrassing defeat, and the media are once again focusing on the Ukrainians’ successes.”