The Russian Embassy has questioned the 'disappointing' decision to deny the visa of former spy Sergei Skripal's niece, as the woman goaded Theresa May in a video message.

The embassy has accused the Foreign Office of failing to answer its questions over why Viktoria Skripal was denied a visa to travel to Britain to visit Sergei and Yulia in hospital.

In a statement, the embassy said the FCO's response to its request for an explanation was 'disappointing' and 'cannot but cause regret'.

The Russian Embassy's harsh words come as Viktoria, 45, blasted the Prime Minister in a video message, saying: 'Dear Theresa May, Please can you as a human being help us to meet our family?

'Why are you destroying our family?... We are ordinary people... Please help us.'

Viktoria has vowed to fight until she can see her cousin and said she would take her case to the United Nations if prevented.

UK authorities refused to grant her a visa, with the Home Office saying her application 'did not comply with the immigration rules', prompting a suggestion from the Russian side that the British had 'something to hide'.

On Sunday the Russian embassy repeated its charge that the decision not to issue a visa was 'politically motivated' and raised questions about the reasoning behind it.

After suggestions to Viktoria that her visa application would be fast tracked, it was refused amid suspicions she is being used as a pawn by the Kremlin.

She has given media interviews questioning Britain's claims that the Russian government was behind the nerve agent attack and said that Yulia's fiance or his family may be the culprits.

She also suggested Sergei and Yulia were poisoned by eating some 'bad fish'.

Viktoria Skripal has made a personal plea to Prime Minister Theresa May

Sergei and Yulia Skripal. The father and daughter are recovering after being poisoned by nerve agent

Last night, Viktoria told this newspaper: 'I see from the refusal that I am not taken by the British side as a member of the family, and therefore I can't come to the UK on behalf of Sergei's mother – who lives with me – to see them.'

And Viktoria told Sky News she wanted to visit the pair in person so she could 'truthfully' report back on their condition to relatives.

'But my visa was rejected,' she said.

'The whole world is now talking about an unprecedented political scandal, but real people are at the epicentre of this scandal. This is our family, which really needs to be together now.

'If Yulia sees this, I want her to see we love her and will always wait for her. I will fight for her till the end.

'If I can't do it here, I will go to the United Nations, and if I can't do it this way, I will walk, I will hitchhike across the border illegally.'