London: Britain and Iran will each appoint a charge d’affaires to work towards resuming ties severed after a mob attacked the British embassy in Tehran in 2011, Foreign Secretary William Hague said Tuesday.

The diplomats, one level below ambassador, will remain in their respective countries but will look into re-opening embassies in London and Tehran, Hague told the House of Commons.

The breakthrough came after Hague met with his Iranian counterpart Mohammad Javad Zarif twice on the sidelines of the UN General Assembly in New York last month, and the pair had a telephone discussion on Monday.

“I’ve made very clear to Mr Zarif that we are open to more direct contact and further improvements in our bilateral relations,” Hague said.

“We have therefore agreed that both our countries will now appoint a nonresident charge d’affaires tasked with implementing the building of relations, including interim steps on the way towards the eventual reopening of both our embassies as well as dialogue on other issues of mutual concern.”

However Hague added: “We must not underestimate the difficulties ahead.”

Hague said the tone of discussions with the Iranians had changed since the election of President Hassan Rouhani in June, and noted resumption of talks planned later this month on Iran’s contested nuclear programme.

Addressing Iran’s disputed nuclear programme, Hague said Tehran would need to make “substantive changes” to it if it wanted the West to ease sanctions, saying the future of British-Iranian relations would depend on tangible steps.

“Iran remains in defiance of six UN Security Council resolutions ... and it is installing more centrifuges in its nuclear facilities,” said Hague.

“In the absence of substantial change to these policies, we will continue to maintain strong sanctions. A substantial change in British or Western policies requires a substantive change in that programme.”

Prime Minister David Cameron welcomed the election of President Hassan Rouhani earlier this year, but said ties remain strained because of the ransacking of the British Embassy in Tehran in 2011, an incident that led to one of the worst crises between the two countries since the 1979 Islamic Revolution.

“We must test the Iranian government’s sincerity to the full, and it is important that our channels of communication are open for that,” said Hague.

British and Iranian officials had already met to discuss the numbers and conditions of locally engaged embassy staff, and would meet again in Geneva next week.