Ecuador has granted citizenship to WikiLeaks founder Julian Assange, who has been holed up in its London embassy for more than five years.

Maria Fernanda Espinosa, Ecuador's foreign minister, told reporters on Thursday that the South American country accepted Assange's application for naturalisation in December.

"What naturalisation does is provide the asylum seeker another layer of protection," she told reporters in Quito.

The Australian-born activist took refuge in the Ecuadorean embassy in the UK capital in 2012 to avoid extradition to Sweden, amid fears that he would have been handed over to the US to face prosecution over the publication of classified military and diplomatic documents by WikiLeaks.

He was wanted in Sweden for questioning over rape accusations. Prosecutors there dropped the case last year, but Assange remained in the embassy after British police said he would still be arrested for violating bail conditions.

Assange posted a photograph of himself wearing a yellow Ecuadorean national football team jersey on Twitter on Wednesday.

Espinosa said Ecuador had asked the UK to grant diplomatic status to Assange in a bid to secure immunity and safe passage, but the request was rejected.

The UK's Foreign Office, in a statement earlier in the day, said, "Ecuador knows that the way to resolve this issue is for Julian Assange to leave the embassy to face justice".

Espinosa said the issue was not about Assange facing British law, but "founded fears that we have about possible risks to the life and integrity of citizen Assange, not necessarily from the United Kingdom, but possibly by third states".

Ecuador was obliged to give him protection as "long as the life, integrity of this protected person could be at risks and danger," she said, adding that her government was exploring other options to resolve the seven-year standoff.