UK hopes to pay £400m debt 'soon', British FM tells Iran

British Foreign Secretary Elizabeth Truss has told Iran she hopes the UK will soon be able to repay its £400m debt to Tehran.

Truss and to her Iranian counterpart, Hossein Amir-Abdollahian, spoke on Monday in a telephone conversation that appeared warmer than expected, an Iranian source was cited by The Guardian as saying.

The debt stems from a cancelled 1970's weapons agreement, in which Iran paid for paid for tanks that were never delivered. The money is believed to be a key sticking point for Iran in discussions relating to the release of British-Iranian nationals it has jailed.During the call, Truss reiterated her determination to secure the release of the British detainees.

The UK Foreign Office has said it is exploring payment options for the historical debt as a matter of urgency.

British Prime Minister Boris Johnson has previously argued Britain's debt is "difficult to settle and square away for all sorts of reasons to do with sanctions" against Iran.

However, some have argued that the UK is responsible for its own sanctions following Brexit and could pay the debt now.

UK-Iranian dual national Nazanin Zaghari-Ratcliffe, who Iran imprisoned on a five-year sentence in 2016 on charges of espionage, is one of the Britons denied the right to leave Iran. Zaghari-Ratcliffe is currently under house arrest in the Islamic Republic.

The mother-of-one expressed concern earlier this month that she has been made a "bargaining chip" in the Vienna negotiations with Iran, stating she feels "anger at her life being stolen".

Other British nationals detained in the country include Anoosheh Ashoori, Morad Tahbaz and Mehran Raoof.

Last December, British government officials travelled to Tehran to discuss clearing the debt, and Iranian ambassador to the UK Mohsen Baharvand was quoted by Guardian as saying he was "hopeful we will reach an agreement".