European countries must overhaul "outdated" laws that let rapists off the hook and perpetuate a culture of victim-blaming, rights groups said Saturday.

Only eight out of 31 countries surveyed by Amnesty International define rape as sex without consent, according to research published on the eve of International Day for the Elimination of Violence against Women.

The rest have legal definitions of rape based on force, threat of force, coercion or the victim's inability to defend themselves.