Spanish construction company Actividades de Construccion y Servicios (ACS) has raised its takeover bid for Leighton Holdings Ltd's (ASX:LEI) parent Hochtief.

This comes a few hours after the German builder recommended that shareholders reject a lower proposal. Hochtief earlier said the initial amount of $3.62 billion was not "adequate from a financial perspective," adding that Credit Suisse and Deutsche Bank support this opinion.

Madrid-based ACS has now increased its bid by 12.5 per cent, offering nine shares for every five shares in Hochtief, up from an earlier offer of eight shares for every five.

The new bid values every Hochtief share at €64.49 ($86.41), based on the closing price of ACS's shares Tuesday.

Hochtief, which has a 54.5 per cent stake in Leighton, said it is examining the sweetened proposal.

The acceptance period is due to end on December 29 and ACS said it is confident it will succeed.

At 1213 GMT, ACS shares lost 2.1 per cent at €35.09. Hochtief shares, meanwhile, gained 1.7 per cent at €65.49.