German automaker Opel, under pressure from its US parent General Motors to cut costs, said Wednesday it will negotiate with unions, but declined to comment on reports of plant closures.

According to the Wall Street Journal, GM has asked Opel to close down two factories, one in Bochum in Germany and another in Ellesmere Port in Britain, employing 3,100 and 2,100 people respectively.

When contacted by AFP, a spokesman for Opel declined to comment, but said the carmaker "must improve earnings, at the level of margins, costs and revenues."

Management and labour representatives "will hold strategic talks", the spokesman added.

For its part, Opel's works council said it had "no information suggesting that GM or Opel would contravene agreements" struck two years ago with the unions that ruled out redundancies or plant closures in Europe before 2014.

Opel suffers from high production costs and is vulnerable to the eurozone crisis, since GM will not allow it to export outside Europe so as not to compete with its own brands.