By Andrew Gray

BRUSSELS (Reuters) - Hungary's prime minister has urged the European Union to start direct discussions with Russia on a ceasefire in Ukraine and drop plans for a joint declaration at an extraordinary EU summit next week, saying differences in the bloc "cannot be bridged".

Under President Donald Trump, the United States has started talks with Russia on ending its war in Ukraine, but without Kyiv or the EU at the table. Trump and Ukrainian President Volodymyr Zelenskiy clashed in a White House meeting on Friday.

In a letter to European Council President Antonio Costa dated Saturday, first reported by German daily Welt and seen by Reuters, Hungarian Prime Minister Viktor Orban said of the EU that there were "strategic differences in our approach to Ukraine that cannot be bridged".

The European Council did not immediately respond to a request for comment.

"I am convinced that the European Union - following the example of the United States - should enter into direct discussions with Russia on a ceasefire and sustainable peace in Ukraine," Orban, a Trump ally, said in the letter.

He said this approach could not be reconciled with the draft conclusions for next Thursday's EU summit, set to focus on additional support for Ukraine, European security guarantees and how to pay for European defence needs.

"Therefore, I propose not to attempt adopting written conclusions on Ukraine," Orban said, alluding to the fact that decisions at EU summits need to be taken unanimously.

Since Russia launched its full-scale invasion of Ukraine in February 2022, Orban has emerged as a vocal critic of EU sanctions against Moscow and the bloc's financial and military support for Ukraine.

Slovakia's Prime Minister Robert Fico is another EU leader who has pushed for fast peace talks. On Saturday, he called the bloc's "peace through force" strategy unrealistic and said the necessity of an immediate ceasefire should be in the EU summit's conclusions.

He also wanted a demand for the reopening of Russian gas transit through Ukraine to be included, after falling into dispute with Kyiv this year when it halted the shipment of gas, forcing Slovakia to find different routes.

"If the summit does not respect that there are other views than continuing the war, the European Council on Thursday may not be able to agree on conclusions on Ukraine," Fico said in a Facebook post.

According to the latest draft statement prepared for the summit, member states were to confirm that there cannot be any negotiations on Ukraine without Ukraine, and that any peace agreement for Kyiv must be accompanied by "robust and credible security guarantees" for the country.

The declaration was also to call for additional military aid.

Friday's clash between Trump and Zelenskiy flared over differing visions of how to end the Ukraine war, with Zelenskiy seeking strong security guarantees from an administration that has embraced diplomacy with Russian President Vladimir Putin.

European leaders lined up afterwards to show solidarity with Ukraine's president.

On Sunday, European leaders will meet in London to discuss a security backstop to any peace agreement between Moscow and Kyiv.

(Additional reporting by Sabine Siebold, Krisztina Than and Jason Hovet, Editing by Timothy Heritage and Barbara Lewis)