In a statement, the ministry noted that UK Defense Secretary Ben Wallace has, himself, confessed to his country’s outstanding debt to Tehran, adding that valid international rulings have also found the UK liable in the case, IRNA reported on Thursday.

International Military Services (IMS), a subsidiary of the British Ministry of Defence, signed contracts in 1971 to sell more than 1,750 Chieftain tanks and armored vehicles to Iran. The deals were canceled after Iran’s monarch Mohammad Reza Shah was deposed during the 1979 Islamic Revolution. Iran, however, had already paid for the tanks, Press TV wrote.

International arbitrators ruled in 2008 that Britain owed the debt that is estimated to stand at £400 million. A previous international ruling had also found that Iran had a right to claim interest on the debt.

The Iranian Defense Ministry’s statement said the IMS refusal to clear the arrears had compelled Iran to resort to international arbitration, adding that the company was still in default of its obligation, although the verdicts have found it liable to pay the debt.

“The relevant authorities in Britain have been trying to shun their responsibility as a liable party on the international arena, especially in the eyes of the Iranian nation,” the statement said.

To try and rationalize their refusal to pay their debt, it added, the UK officials have been citing the United States’ illegal and oppressive sanctions that have come to target the Islamic Republic.

“London is expected to take practical and expeditious steps [in this regard] in order not to further prolong the Iranian government and nation’s dissatisfaction and consternation against England,” the ministry said.

The ministry, meanwhile, denied any link between the case and the issue of Nazanin Zaghari, who was arrested for spying by Iran’s intelligence authorities in April 2016 as she was trying to leave for the UK.

Zaghari was handed a five-year jail term after being found guilty of spying and spreading propaganda against the Islamic Republic.