A UK family of 12 who went missing have joined so-called Islamic State and are "safer than ever", according to a statement said to be on their behalf.

The statement, purportedly sent by a member of IS, said it was "outrageous" to suggest the family had been kidnapped and forced to join the group.

It called on all Muslims to join them and "hasten to the obedience of Allah".

The family from Luton has not been seen since 17 May and includes three children aged between one and 11.

Police have previously said they may have travelled to Syria.

The BBC has not been able to independently verify if the statement, which includes two photos purportedly of family member Muhammed Abdul Mannan, is genuine.

The missing family is:

• Muhammed Abdul Mannan, 75, and his wife Minera Khatun, 53
• Their daughter Rajia Khanom, 21, and sons Mohammed Zayd Hussain, 25, Mohammed Toufique Hussain, 19, Mohammed Abil Kashem Saker, 31, and his wife Sheida Khanam, 27
• Mohammed Saleh Hussain, 26, and his wife Roshanara Begum, 24, along with three children, aged between one and 11

Mohammed Saker is missing aged 31. Photo: Bedfordshire Police/BBC

Mohammed Toufique Hussain is aged 19. Photo: Bedfordshire Police/BBC

Another family member missing is Mohammed Zayd Hussain. Photo: Bedfordshire Police/BBC

The statement, passed to the BBC by a Briton fighting with IS, said the family had arrived in a land that was "free from corruption and oppression" and had not been "commanded" to join by a single person but by the "Khalifah of the Muslims".

It said: "We say to those that are concerned for our safety to put your hearts at rest for we feel safer than we have ever felt before.

"We call all Muslims to rush to the command of your Khalif. Race to your state. Race to what will give you honour in this life and the hereafter."

The Islamic State group has seized large swathes of Iraq and Syria since last June, becoming notorious for its brutality, including mass killings, abductions and beheadings.

On 29 June 2014 it announced the formation of a caliphate - a state governed in accordance with Islamic law or Sharia, by God's deputy on Earth, or caliph.

The family was reported missing to police by two sons, understood to be Mannan's from a previous marriage, who live in Luton.

Ashuk Ahmed said he had known the family for 35 years. Photo: Bedfordshire Police/BBC

The family flew to Bangladesh on 10 April, police said, and then to Istanbul on 11 May.

They were due back at Heathrow three days later but failed to return.

It is believed Khanom had links to banned Islamist group al-Muhajiroun, which had members in Luton.

Neighbour Syed Hussain said police had visited the family's house. Photo: Bedfordshire Police/BBC

It comes after three sisters reportedly travelled to Syria with their nine children.

Sisters Khadija, Sugra and Zohra Dawood and their children went missing on 9 June, and an IS smuggler has since told the BBC they have reached Syria.