European Union and Turkish leaders may announce a behind-the-scenes agreement later this week to resettle 400,000 to 500,000 Syrian refugees directly from Turkey to the EU, Hungarian Prime Minister Viktor Orban said on Wednesday.

Orban has locked horns with EU partners for years over economic policy, political freedoms and most recently the handling of the migrant crisis, in which the Hungarian leader took a hard line and erected a steel fence along the country's southern border to keep out migrants.

Hungary has firmly resisted the idea of resettlement quotas to distribute more evenly the migrants, most of whom wanted to go to Germany or Sweden.

Speaking to a meeting of Hungarian leaders in Budapest, Orban said he expected intense pressure from Europe to accept some part of those half a million refugees, something he said Budapest could not do.

He added that the agreement has already been floated at a recent EU summit in Malta but was abandoned and not included in the EU-Turkey agreements signed at the weekend in Brussels after its proponents could not gather the necessary support for it.

"The issue (of resettlement) will be a hot potato in the coming period because even though this could be kept in a semi-secret state... someone somewhere - I think in Berlin this week - will announce that 4-500,000 Syrian refugees could be brought straight from Turkey to the EU," Orban said.

"This nasty surprise still awaits Europeans."

He alluded to the deal being orchestrated by Germany, and said it could frame the political discourse in Europe in the next few days and weeks.

"The pressure will be intense on us and the other Visegrad Four countries (Poland, Slovakia and the Czech Republic)," he said.

"They will portend that once the agreement is made by certain parties - and to avoid diplomatic complications I will not tell you which country Berlin is in - we should not only bring these people to Europe but divide them amongst ourselves, as an obligation."

"It will not be an easy one because obviously we cannot accept it like this."