LONDON (Reuters) - Britain could introduce new legislation to make it easier to sanction Russian oligarchs, a government source said, after the government has struggled to find evidence to justify targeting individuals with links to President Vladimir Putin.

       Britain has so far imposed sanctions on nine wealthy Russians since Putin invaded Ukraine and Prime Minister Boris Johnson has been accused by opposition politicians of failing to take more action.

       The European Union on Monday imposed sanctions on 26 prominent people over Russia's invasion of Ukraine, including oligarchs and people active in the oil, banking and finance sectors.

       (Reporting by Andrew MacAskill; editing by William James)