The firm said falling demand in the US had intensified competition and put pressure on margins.
The warning statement said: “This, combined with the impact of the adverse weather conditions in the first quarter, means that the board expects the result from the group’s US businesses in the first half of 2010 to be around breakeven and the full year US result to be well below our expectations.”
The firm said that the UK business remained profitable, despite operating in one of the most difficult trading environments it had seen.
Keller said across the group there were early signs of a return to turnover growth, but it would be some time before margins recovered.
This year’s orders intake to April was 9% ahead of last year and had grown each month.