American Marconi Wireless News - Ukraine says fighting 'difficult' after reports of Russia's rapid gains

The gains came just days before US President Donald Trump was to meet Russian counterpart Vladimir Putin in Alaska for talks on the war, the first meeting between a sitting US and Russian leader since 2021.

The Ukrainian army said it was engaged in "heavy" battles with Russian forces attempting to penetrate its defences.

"The situation is difficult and dynamic," it said in a statement.

A map published by Ukrainian battlefield monitor DeepState, which has close ties with Ukraine's military, showed Russia had advanced around 10 kilometres (six miles) over around two days, deep into a narrow section of the eastern front line.

The corridor -- now apparently under Russian control -- threatens the town of Dobropillia, a mining hub that civilians are fleeing and that has come under Russian drone attacks.

It also further isolates the destroyed town of Kostiantynivka, one of the last large urban areas in the Donetsk region still held by Ukraine.

- 'New offensive operations' -

The Institute for the Study of War, a US-based observatory, said Russia was sending small sabotage groups forwards.

It said it was "premature" to call the Russian advances in around Dobropillia "an operational-level breakthrough".

The military's Operational-Tactical Group Donetsk, which oversees parts of the front in the industrial region, also said Russia was probing Ukrainian lines with small sabotage groups, describing battles as "complex, unpleasant and dynamic".

Trump has described his summit with Putin on Friday as a chance to check the Russian leader's ideas for ending the war.

Ukrainian leader Volodymyr Zelensky warned ahead of the talks that Moscow was laying the groundwork for further attacks, after Trump said on Monday that both sides would have to swap territory for peace.

European leaders have meanwhile sought to ensure respect for Kyiv's interests.

"We see that the Russian army is not preparing to end the war. On the contrary, they are making movements that indicate preparations for new offensive operations," Zelensky said in a statement on social media.

Russia, which invaded Ukraine in 2022, has made costly but incremental gains across the sprawling front in recent months and claims to have annexed four Ukrainian regions while still fighting to control them.

Ukrainian police meanwhile said that Russian attacks in the past hours had killed three people and wounded 12 others, including a child.

Ch.Kahalev--AMWN