President Volodymyr Zelensky said he had ordered Ukraine’s military leaders to respond after a series of Russian attacks targeting railway infrastructure and logistics routes.

His comments on Monday came after Russian forces stepped up attacks, including an attack on a train in the eastern region of Kharkiv last week that killed five people on board.

Despite nearly four years of war, Ukraine has managed to keep its national rail network operational. Russian forces have prioritized capturing train hubs such as Kupinsk and Pokrovsk in eastern Ukraine.

“The Russian army remains focused on terrorist activities against our logistics facilities – mainly railway infrastructure,” Zelensky said in a post on social media. “Especially there were strikes in the Dnipro region and Zaporizhia, specifically targeting railway facilities.”

Ukraine’s state railway operator has warned that several of its lines in eastern Ukraine are becoming increasingly “high-risk” and urged passengers to take buses instead.

In the eastern region of Sumy, Uzbekistan said it would monitor threats from Russian drones and block trains if such threats were seen near air raid shelters.

‘Very complex’ negotiations

Russian drones and missiles continue to bomb civilian areas, with the latest major airstrike on Sunday killing 12 miners inside a bus. The barrage also disrupted Ukraine’s power grid, leaving people without heat, lighting and running water during the cold winter.

These attacks are carried out as A new round of negotiations brokered by the United States Conference to end the war will continue this week after a brief postponement. Kremlin spokesman Dmitry Peskov said discussions would take place on Wednesday and Thursday in Abu Dhabi, the United Arab Emirates, where a meeting was held last month.

On Sunday, Zelensky said he would send a delegation.

U.S. President Donald Trump’s administration has spent the past year pushing both sides to find compromises to end the war. But as the fourth anniversary of Russia’s full-scale invasion of its neighbor approaches this month, breaking the deadlock on key issues appears no closer.

Peskov described the negotiations as “very complex.”

“On some issues we do get closer because there’s discussion, dialogue, and it’s easier to find common ground on some issues,” he told reporters. “There are some issues where it’s harder to find common ground.”

russian envoy Kirill Dmitriev in Miami, FloridaTalks were held over the weekend with U.S. officials, but Peskov declined to provide any details of the meeting.

A key sticking point is whether Russia can hold on to the Ukrainian territory its troops have captured, particularly the industrial heartland of eastern Ukraine. Moscow also claims other Ukrainian lands it failed to seize on the battlefield.

Ukraine has ruled out giving up territory, saying such a move would only embarrass Moscow and refusing to sign any deal that might not prevent another Russian invasion.

After failing in its goal of launching a lightning offensive to seize Kiev and overthrow Ukraine’s leadership in a matter of days in 2022, Russia has been hamstrung by Ukraine’s defenses and is now making an arduous advance at a huge human cost.