Russian troops have reportedly been usinf underground gas pipelines to carry out an incursion into the Ukrainian-held Kursk town of Sudzha.

The US-based Institute for the Study of War told Newsweek that sources in both Ukraine and Russia reported Russian attempts to outflank Ukrainian troops in Sudzha, which lies around 6 miles from the border, through an underground gas pipeline. On Saturday, Moscow said that Russian troops had captured three settlements in Kursk, and on Sunday said that the Kursk village of Lebedevka, northwest of Sudzha, had been seized as well.

One Russian military blogger said that troops from Russia crawled inside miles of pipeline tunnels, and often sat and waited "for the command to storm for several more days." Images shared by pro-Russia accounts, which Newsweek said it could not independently verify, reportedly showed Russian soldiers inside the pipelines.

The General Staff of the Armed Forces of Ukraine wrote on Saturday that Russian forces were detected "moving along a gas pipeline branch in an attempt to gain a foothold" near Sudzha and Ukrainian forces deployed rocket and artillery strikes against them. 

According to the Associated Press, Russia had used the pipelines until recently to send gas to Europe. Sudzha, which had around 5,000 residents prior to Russia’s invasion of Ukraine in 2022, houses major gas transfer and measuring stations.

This comes as Ukrainian officials and US negotiators are set to meet in Saudi Arabia on Tuesday to discuss a possible peace deal in the region. Ukrainian President Volodymyr Zelensky has sent an apology letter to President Donald Trump after a White House meeting grew tense, with the Ukrainian leader being thrown out and a mineral agreement between the two nations left unsigned.