KYIV (Reuters) - Ukrainian President Volodymyr Zelenskiy appealed to U.S. President Joe Biden and Chinese leader Xi Jinping on Sunday to join an upcoming peace summit as his country struggles to stave off unrelenting attacks by Russia in its 27-month-old invasion.

Moscow's forces have in recent weeks advanced on the battlefield and stepped up air strikes on cities, and Kyiv hopes the June meeting in Switzerland will help pile international pressure on Russian President Vladimir Putin.

In English-language video recorded inside the charred remains of a printing press destroyed on Thursday in a Russian air strike, Zelenskiy said the summit would "show who in the world really wants to end the war".

"I am appealing to the leaders of the world who are still aside from the global efforts of the Global Peace Summit - to President Biden, the leader of the United States, and to President Xi, the leader of China," he said.

"Please, show your leadership in advancing the peace - the real peace and not just a pause between the strikes.

Russia has said it sees no point in the conference to which Moscow is not currently invited.

Zelenskiy's comments came two days after Russian sources told Reuters that Putin was ready to halt the war in Ukraine with a negotiated ceasefire that recognises the current battlefield lines.

Zelenskiy and Ukraine's supporters say a ceasefire will only help Russia rearm and regroup.

Russia has in recent months made slow but steady gains along several parts of the sprawling eastern front and is attempting to push deeper into the northeastern Kharkiv region after a ground incursion launched earlier this month.

In an interview with Reuters last week, Zelenskiy said it was crucial to get as many countries around the table at the peace talks as possible. Putin has said he believes the talks may convert Ukrainian demands for a Russian withdrawal into an ultimatum for Russia.

(Reporting by Dan Peleschuk; Editing by Toby Chopra)