UPDATE 1-EU executive to tighten market abuse rules

* European Commission says rules need tightening

* Catching abusers has proved difficult since law introduced

* Document sees possibility of widening scope of rules

(Adds more details)

By Huw Jones

BRUSSELS, April 20 (Reuters) - European Union rules designed to stamp out market abuses by share dealers need tightening to help improve investor confidence, the bloc's executive body said on Monday.

The rules, introduced in mid-2005, were aimed at preventing market manipulation and insider dealing.

But catching abusers has proved difficult, even though they would be considered civil cases under the EU law, mostly requiring a lower burden of proof than for criminal charges.