US Republican front-runner Donald
Trump has dropped his pledge to support the party candidate if he does
not win the nomination for the November election.
Mr Trump's rivals, Ted Cruz and John Kasich, refused to say outright whether they would unite behind a nominee. All the Republican candidates signed a loyalty pledge last November.
It is the latest sign of friction between Mr Trump and Mr Cruz, who have been embroiled in a dispute involving each other's wives.
A committee supporting Mr Cruz published a nude photo of Mr Trump's wife Melania from 2000. In retaliation, Mr Trump tweeted an unflattering picture of Mr Cruz's wife Heidi.
Mr Trump claims he has been "treated very unfairly" by Republican party leaders - some have expressed disquiet or downright opposition to him winning the nomination.
To a question about whether he maintained his loyalty pledge from last November, Mr Trump said: "No, I do not any more."
At the time of the pledge, Trump had said: "I have no intention of changing my mind."
