A picture purportedly showing Sheikha Latifa at Madrid's airport has emerged, the latest in a series of images posted after the UN asked for proof the Emirati royal was still alive.

The UN human rights office asked for evidence about Dubai's ruler Sheikh Mohammed bin Rashid Al-Maktoum's daughter in February.

It came after the BBC aired a video shot by Latifa saying she was being held captive and feared for her life.

Sheikh Mohammed is the vice president and prime minister of the United Arab Emirates, of which Dubai is one of the seven emirates.

His 35-year-old daughter made an unsuccessful attempt to flee the emirate in March 2018, escaping by boat with the help of friends before being hauled back.

She has not been seen in public since then.

AFP news agency is unable to verify the latest photograph or when it was taken.

It was published today on an account belonging to a woman that British media have identified as Sioned Taylor, a former Royal Navy member.

It showed the two women standing side-by-side, wearing masks, near an airport tarmac.

A caption read: "Great European holiday with Latifa. We're having fun exploring!"

In the comment section, the account's handler responds "well spotted" to an inquiry as to whether the picture was taken at Madrid's Barajas airport.

Dubai authorities did not immediately respond to requests for comment on the photograph.

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Last month, the same account published two pictures purportedly showing Sheikha Latifa -- one in a restaurant and another in a Dubai shopping centre.

According to the BBC, friends of Latifa have said they recognised the two women seen in the shopping centre image, and that the royal is acquainted with them.

A London-based group that has campaigned for her freedom said the release of the photographs was encouraging.

"We say we are pleased to see Latifa seemingly having a passport, travelling and enjoying an increasing degree of freedom, these are very positive steps forward," said David Haigh, co-founder of the Free Latifa campaign.

"I can also confirm that several of the campaign team have been contacted directly by Latifa," he added in a statement.

In February, Dubai's royal family released a statement insisting Latifa was being "cared for at home".

"Her family has confirmed that her highness is being cared for at home, supported by her family and medical professionals.

"Sheikha Latifa continues to improve and we are hopeful she will return to public life at the appropriate time."