Donald Trump may have his eyes on running against Hillary Clinton in the general election, but in the meantime he's stepping up attacks on America's most watched female news anchor Megyn Kelly.

Having threatened riots should the US Republican party deny him the nomination in the race for the White House, Trump took time out of his busy schedule on Thursday to fire off three tweets calling out "crazy" Megyn Kelly.

First, he complained that she hosted his closest Republican rival, Ted Cruz, whom he has nicknamed "lyin' Ted" on her prime-time Fox News show The Kelly File, the second most watched program in American cable news after that of fellow Fox anchor Bill O'Reilly. In the morning, he complained about an interview in which Kelly said O'Reilly could have done more to defend her against Trump. "Her bad show is a total hit piece on me. Tough!" he said.

Trump regularly posts messages from others who denigrate Kelly. The avalanche of criticism prompted one of Kelly's colleagues to hit back. Senior meteorologist at Fox News, Janice Dean tweeted:

The feud began early in January, when Trump withdrew from Republican debate with party rivals out of anger at host Kelly.

Even after he won the Florida primary on Tuesday, a crushing victory that forced rival Marco Rubio to withdraw from the race, Trump had the knives out for Kelly calling her "crazy" and "unwatchable".

Kelly brushed off the vitriol in an interview with More magazine, in which she said she found inspiration from Britain's first female prime minister, dubbed the Iron Lady for her fortitude. "I've been thinking about that Margaret Thatcher quote where she said something like, 'I love when they attack me personally because it means they don't have a political argument left,'" she was quoted as telling the magazine.

A former corporate litigator, Kelly was in 2014 the only woman journalist listed on the TIME 100: The Most Influential People in the World list.