Diplomats began to broker a deal to move Julian Assange out of the Ecuadorean embassy in London more than a year ago and sought assurances he would not be extradited to a country where he could face the death penalty.

Ecuador's president, Lenin Moreno, was assured by two British foreign secretaries that Julian Assange would not be extradited to a country where he could face the death penalty, according to letters seen by the Guardian.

Assange, 47, was taken from Ecuador's London embassy by British police last Thursday after the country withdrew his political asylum, ending a stay of almost seven years.

ABC News reported this week that the challenge the Ecuadorans faced in turning him over to British officials was the prospect of Assange facing the death penalty, which Ecuador strongly opposes.

Letters signed by the foreign secretary, Jeremy Hunt, and his predecessor Boris Johnson, dated March 7, 2018, and Aug 10, 2018, respectively, confirm a person cannot be extradited if they could face the death penalty, according to British legislation.

Assange is expected to fight extradition to the US over an allegation he conspired with former army intelligence analyst Chelsea Manning to break into a classified government computer. Sweden is also expected to decide whether to reopen an investigation into rape and sexual assault allegations against him.

Assange already faces up to 12 months in prison in the UK after being found guilty of breaching his bail conditions when he entered the Ecuadorean embassy in 2012.

He moved into the embassy after losing his battle against extradition to Sweden where he faced the allegations, including rape.

Assange is charged by the US with one count of conspiracy to commit computer intrusion with Manning. The ABC report claimed US Justice Department officials would not confirm that the US agreed to take any sentence off the table.

But it was noted that the charge the US unsealed against Assange does not represent a capital offense and carries a maximum of five years in prison. The Justice Department has 60 days from the time of the request for extradition to add any charges and would not comment on future charges.

There are only 41 US federal offenses punishable by the death penalty. Nearly all of them have to do with murder or death resulting from some other crime or action. Two notable exceptions are treason and espionage.

Six months after Ecuador's first approach to the UK for assurances in March, the country's ambassador to Germany, Manuel Mejia Dalmau, sought a private "emergency meeting" in Berlin with the US ambassador to Germany, Richard Grenell, viewed as one of US President Donald Trump's closest envoys in Europe, the officials said.

During one meeting, Dalmau asked whether the US would commit to not putting Assange to death, according to a senior US official.

Grenell then contacted the US Justice Department to see if he could provide assurances that the US government would not seek the death penalty.

Deputy Attorney General Rod Rosenstein agreed to the request. That enabled Grenell to make the pledge.