LONDON - Europe's natural gas derivatives markets has become less transparent since Russia's invasion of Ukraine and is vulnerable to concentration and liquidity risks, the European Union's securities watchdog said on Friday.

"The market is characterised by a high degree of concentration of market participants active in clearing and trading activity, and some energy firms hold relatively large derivative positions," ESMA said in a study.

(Reporting by Huw Jones; Editing by Toby Chopra)