Former US President Donald Trump says he expects to be arrested on Tuesday in a case that involves him allegedly paying hush money to a porn star before the 2016 presidential election.

In a post on his Truth Social platform on Saturday, Trump called on his supporters to protest ahead of his alleged arrest. But there has been no official confirmation of the likelihood or timing of charges being brought.

"Illegal leaks from a corrupt & highly political Manhattan district attorney's office ... indicate that with no crime being able to be proven ... the far & away leading Republican candidate & former president of the United States of America, will be arrested on Tuesday of next week," Trump wrote on Truth Social.

The probe comes as Trump seeks the Republican nomination for the presidency in 2024.

His message seemed designed to preempt a formal announcement from prosecutors and to galvanize outrage from his base of supporters in advance of widely anticipated charges. Within hours, his campaign was sending fundraising solicitations to his supporters, while influential Republicans in Congress and even some declared and potential rival candidates issued statements in his defense.

In a later post that went beyond simply exhorting loyalists to protest about his legal peril, the 2024 presidential candidate directed his overarching ire in all capital letters at the Biden administration and raised the prospect of civil unrest: “IT’S TIME!!!” he wrote. “WE JUST CAN’T ALLOW THIS ANYMORE. THEY’RE KILLING OUR NATION AS WE SIT BACK & WATCH. WE MUST SAVE AMERICA!PROTEST, PROTEST, PROTEST!!!”