European Council chief Charles Michel expressed confidence Wednesday that the European Union would reach an agreement on a Russian oil embargo ahead of next week's European summit, despite opposition from Hungary.

Michel said European leaders were working very hard to find a resolution, adding that he had had many contacts on the subject.

"I'm still confident that we can be able to resolve the topic before the European Council" meeting in Brussels on Monday and Tuesday, Michel said during a joint press conference in Stockholm with Swedish Prime Minister Magdalena Andersson.

Hungary has yet to be convinced to back an EU embargo on Russian oil, and bringing it up at next week's European summit would be pointless, Prime Minister Viktor Orban told Michel earlier this week in a letter seen by AFP.

"Looking at the gravity of the issues still open, it is very unlikely that a comprehensive solution could be found before the special meeting of the European Council on 30-31 May," Orban wrote in the letter, dated Monday.

"I am convinced that discussing the sanctions package at the level of leaders in the absence of a consensus would be counterproductive," it said. 

Michel said Wednesday he was "realistic, I know that there are difficulties" but that he would "propose some possible solutions".

Some diplomatic sources have suggested EU leaders might take up the issue at the Brussels summit in order to come to a political agreement to unblock technical talks underway between Hungary and the European Commission.

Orban, often the odd man out in EU decision-making, has rocked the bloc's unity on the war in Ukraine by opposing an oil embargo. 

Landlocked Hungary relies on Russian oil from a single pipeline and Orban insists the proposed sixth package of EU sanctions against Moscow would have a devastating impact on his country's economy.