Britain said on Thursday that moves towards paying half a billion dollars to Iran as a debt had nothing to do with a bid to secure the release of a jailed Iranian-British aid worker. Nazanin Zaghari-Ratcliffe, a project manager with the Thomson Reuters Foundation, was detained in April and sentenced to five years after an Iranian court convicted her of plotting to overthrow the government. She denies the charges. British officials did not directly answer requests for comment on whether they were preparing to pay the money to Iran - as part of a debt that dates back to an arms contract for which Britain had received an advance payment from Iran but which was halted in 1979 - but British PM Theresa Mays spokesman said the debt issue was not linked to the attempts to convince Tehran to release Zaghari-Ratcliffe. "It is wrong to link a completely separate debt issue with any other aspect of our bilateral relationship with Iran," a government spokesman said. Iran also rejected media reports associating the debt Britain owed to Iran with the fate of Zaghari-Ratcliffe. "These are two separate matters ... Linking them is wrong. Nazanin Zaghari-Ratcliffe has been tried and sentenced to jail," TV quoted Foreign Ministry spokesman Bahram Qasemi as saying. Johnson has faced calls to resign over his handling of the case, after saying last week that Zaghari-Ratcliffe was training journalists in Iran. Johnson later told MPs she was on holiday visiting family but his earlier comments were seized upon by the Iranian judiciary to justify her detention.