A British-Iranian mother detained in Tehran is set to begin a three-day hunger strike in protest against being denied specialist medical care, her husband says.

He said prison officials had refused to let Nazanin Zaghari-Ratcliffe see a doctor to examine lumps in her breast and other health issues.

Richard Ratcliffe said she will consider extending the hunger strike if her demand is not met.

Zaghari-Ratcliffe has been imprisoned in Iran for more than 1,000 days.

A project manager with the Thomson Reuters Foundation, she is serving a five-year prison sentence for allegedly plotting to overthrow Iran's clerical establishment, a charge she and her family have denied.

Ratcliffe told The Observer newspaper that his wife was having medical treatment blocked for checking lumps in her breasts, neurological care over her neck pains, and numbness in her arms and legs, as well as for seeing an outside psychiatrist.

The head of the Thomson Reuters Foundation, Monique Villa, said she was "sincerely worried" about Zaghari-Ratcliffe going on hunger strike on January 14.

Villa said in a statement that her "health is already at its poorest"

Zaghari-Ratcliffe was arrested at Tehran airport in April 2016 while traveling home with her daughter.

Her employer and the British government say she was in Iran visiting relatives.

British officials have routinely sought Zaghari-Ratcliffe's release in talks with Iranian leaders.

Zaghari-Ratcliffe was briefly reunited with her 4-year-old daughter, Gabriella, during a three-day temporary release in August.

Based on reporting by the BBC and AP