LONDON, Sept 23 (Reuters) - British Foreign Secretary Dominic Raab said it would be beyond the pale for Iranian-British aid worker Nazanin Zaghari-Ratcliffe to be returned to detention in Iran at this time.

He added that Britain was still enagaged in a process of paying back a debt it owns to Iran but that this was "not linked but in parallel" to the legal case.

"There's been a process that has been ongoing," he told Sky News about the debt dating back to 1979. "It's not linked but it's in parallel, where we've been saying look we recognise this debt and we'll look at how we can resolve it as best we can.

"Frankly that is separate from the clear and immediate obligation on the right to not to detain British nationals.

"It will be beyond the pale, for her to be returned to detention at this time."

Zaghari-Ratcliffe is a project manager with the Thomson Reuters Foundation.