Belgium will raise Opel's restructuring at a European Union summit on Thursday amid the row over German state aid, the head of the country's Flanders regional government said on Wednesday.

"I don't have an agenda for tomorrow, but I think it will certainly be a subject for discussion, informally and perhaps formally," Flanders minister-president Kris Peeters told news agency AFP.

He said he had talked earlier with Belgian prime minister Herman Van Rompuy, hoping he would pass a message to German chancellor Angela Merkel.

The Opel plant in Antwerp, Belgium, is now seen under threat in General Motors' planned sale of Opel to a consortium led by Magna International.

Speaking after meeting EU competition commissioner Neelie Kroes, Peeters said a formal complaint for an investigation into allegations the German aid was protectionist was being considered.

"We are looking into that," he said.

Officials are still waiting for a series of reports on Magna's planned takeover of Opel and the rest of GM's Europe division, which employs 50,000 people across Europe.

Peeters added that Kroes had promised a "severe" examination of the case and that if she found "political factors" had been at work, "there would be a very strong and very clear conclusion."