Donald Trump has labelled Hillary Clinton "crooked" and says he cannot wait to face her in November's US presidential election.

Trump's latest outburst came on the same day an internal government watchdog ruled Hillary Clinton's work as US Secretary of State - on a private email server - broke government rules.

Speaking at a rally to supporters in Anaheim, California, the likely Republican nominee said: "She's as crooked as they come".

The State Department inspector general was the first official audit of the email server to be made public.

Donald Trump said the the report was "not so good", as it concluded Clinton would not have been allowed to use the server in her home even if she had asked for approval.

The report also added that staff who raised concerns were told to keep quiet.

Aware of the potential damaging fall-out from the investigation, he said: "I want to run against Hillary. [But] it could be that we run against crazy Bernie".