Iran has postponed a new trial due to start Sunday of Nazanin Zaghari-Ratcliffe, a British-Iranian woman detained in Tehran for sedition, her husband said.

"Yes, today's hearing was postponed," Richard Ratcliffe told AFP in London. Her Iranian lawyer was told "the case was not happening today", he added.

Zaghari-Ratcliffe, 41, has spent more than four years in jail or under house arrest since being arrested in the Iranian capital in April 2016 while on a visit to see relatives with her young daughter.

Iranian state television's website Iribnews said on Tuesday that she and her lawyer had been notified of a new indictment, without giving further details or a trial date.

Ratcliffe had said last week that she was due to appear in court on Sunday, and that it was "increasingly clear" she was being held as a "hostage" against a longstanding UK debt to Iran.

Zaghari-Ratcliffe, who worked for the Thomson Reuters Foundation -- the media organisation's philanthropic arm -- denied sedition but was convicted and jailed for five years.

Her British MP Tulip Siddiq also relayed the news of Sunday's postponement after speaking to Ratcliffe.

"She is relieved, frustrated, stressed and angry. Once again she's being treated like a bargaining chip," Siddiq tweeted.