The European Union is against making any unconditional invitation to Russia to let it rejoin talks among the G-7 world leaders, a senior official with the bloc said of an idea floated by U.S. President Donald Trump.

The seven leaders of the world's advanced industrialized countries are due to meet in the French resort of Biarritz this weekend.

The format used to be known as G-8 before Russia was kicked out in 2014 after annexing Crimea from Ukraine and then backing an anti-Kiev rebellion in the industrial east of the country.

The official, speaking on condition of anonymity ahead of the G-7 summit, said the reasons for excluding Moscow "remain valid" and that any unconditional return offer would be "counterproductive" and "a sign of weakness."

Ukrainian President Volodymyr Zelenskiy also voiced his opposition to the idea.

"Since March 2014, when Russia was suspended from the G-8, nothing has changed. The Ukrainian Crimea is still occupied, the Ukrainian Donbas is still suffering from the war," Zelenskiy tweeted early Thursday.

In Berlin on Wednesday, German Chancellor Angela Merkel and visiting British Prime Minister Boris Johnson poured cold water on the idea of readmitting Russia soon.

Merkel said progress would first be needed on Ukraine.

Johnson agreed, adding: "Given what happened in Salisbury ... given the use of chemical weapons on British soil, given the continuing instability, the civil war in Ukraine, given Russia's provocation not just in Ukraine but in many other places ... the case has yet to be made out for Russia to return to the G-7."