Ukraine faces increasing difficulties in its fight against Moscow’s invasion, the country’s top military commander, Col Gen Oleksandr Syrskyi, said on Saturday, as Russian forces advance and North Korean troops prepare to join the Kremlin’s campaign. Writing on Facebook, Syrskyi said he told the head of the US European command, Gen Christopher Cavoli: “The situation remains challenging and shows signs of escalation. The enemy, leveraging its numerical advantage, is continuing offensive actions and is focusing its main efforts on the Pokrovsk and Kurakhove directions.”

Ukraine’s general staff, in a late evening report on Saturday, said 40 armed clashes had occurred around villages near Kurakhove. Both Ukrainian and Russian military bloggers on Friday said Russian forces sought to encircle the city. “We have numerous reports of North Korean soldiers preparing to participate in combat operations alongside Russian Forces,” Syrskyi said.

The EU foreign policy chief, Josep Borrell, has pledged “unwavering” support for Ukraine in Kyiv on Saturday. He said “the clear purpose” of his visit to Ukraine is to “express European Union support to Ukraine – this support remains unwavering”. “This support is absolutely needed for you to continue defending yourself against Russia aggression.”

The Trump administration’s priority in Ukraine would be establishing peace and not restoring lost territory, including Crimea, a senior aide to the US president-elect has said. Bryan Lanza, a longtime Republican party strategist, told the BBC that Donald Trump’s administration would be asking the Ukrainian president, Volodymyr Zelenskyy, for a “realistic vision for peace”. “And if President Zelenskyy comes to the table and says, ‘well we can only have peace if we have Crimea’, he shows to us that he’s not serious. Crimea is gone,” Lanza said.

Trump’s transition team has distanced the incoming president from Lanza. “Bryan Lanza was a contractor for the campaign,” said a spokesperson. “He does not work for President Trump and does not speak for him.”

Ukraine’s foreign minister, Andrii Sybiha, has said Kyiv is ready to work with the Trump administration. “Remember that President Zelenskyy was one of the first world leaders … to greet President Trump,” Sybiha told reporters. “It was a sincere conversation [and] an exchange of thoughts regarding further cooperation. Also during the telephone conversation, further steps to establish communication between teams were discussed and this work has also begun. Therefore, we are open for further cooperation and I’m sure that a unified goal of reaching just peace unites all of us.”

The Russian deputy foreign minister, Sergei Ryabkov, said Moscow and Washington were “exchanging signals” on Ukraine via “closed channels”, without specifying whether the communication was with the current administration or Donald Trump’s incoming administration. Russia is ready to listen to Trump’s proposals on Ukraine provided these were “ideas on how to move forward in the area of ​​settlement, and not in the area of ​​further pumping the Kyiv regime with all kinds of aid”, Ryabkov said on Saturday in an interview with Russian state news agency Interfax.

Sergei Ryabkov has said Russia’s updated nuclear doctrine would make it possible “to turn to the nuclear option” if there was an acute crisis in relations with the west and the situation in Ukraine, Interfax reported. “This process will be finalised,” Russia’s deputy foreign minister said. “The president of the Russian Federation as supreme commander-in-chief will undoubtedly make decisions that will mean the improvement of the conceptual foundations of our activities in this sphere.”

A possible agreement between Donald Trump and Vladimir Putin to end the war in Ukraine poses “a serious challenge for everyone”, the Polish prime minister, Donald Tusk, has warned. “There is no doubt that this new political landscape is a serious challenge for everyone, especially in the context of a possible end to the Russian-Ukrainian war as a result of an agreement between, for example, the president of Russia and the new president of the United States,” Tusk said as he prepared to meet with the Nato head, Mark Rutte, the French president, Emmanuel Macron, and the British prime minister, Keir Starmer.

Ukrainian drones struck a munitions factory in central Russia in an overnight attack, a source in Ukraine’s SBU security service told Reuters on Saturday. The attack on the Aleksinsky chemical plant, which produces gunpowder, ammunition and weapons in the Tula region about 200km (120 miles) south of Moscow, was part of a strategy to target factories that support Moscow’s war against Ukraine, the source said. “Attacks on weapons warehouses, military airfields, and enterprises, which are part of the Russian military-industrial complex, reduce Russia’s ability to terrorise our country,” the SBU source said.