A father has stepped up the hunt for his daughters - missing in Thailand for 72 days.

Ananya (known as Annie), now 11 and Aleena Day, aged six, were reported missing on Sunday, June 1 and their father Robert Day has been searching for them ever since.

The sisters from Sevenoaks were on a trip to see their mother Onwarat Gamlem in Pattaya, who separated from their father Robert Day in 2010, but did not return to him on Sunday, June 1 as planned.

An arrest warrant has been issued for the girls’ mother on suspicion of abducting her daughters.

Over two months on, Mr Day has taken new steps in his attempt to trace them down by hiring advertising vans with posters of them on to travel around the Chonburi Province.

The vans play a recorded message advertising a reward of 100,000 baht, equal to £2,000, for anyone who returns them.

They also play two songs - Ananya’s favourite song, Beautiful Girl, and the well-known Santa Claus is Coming to Town, which Mr Day hopes will draw public attention.

It has been reported in Thai press that the police received a phone call from an unknown caller offering to return the children if their mother, Onwarat, was given full immunity.

However, the family have not had any further correspondence with the caller, and fear it was not legitimate.

Mr Day's sister, Charlotte Dillow has been supporting the family in their search, she said: “I think my whole family fears that it was a hoax call. There has been no resolution to this dreadful situation.

"My brother is absolutely heartbroken at being separated from his girls but is determined to stay in Thailand until they are found.”

As a result of strict Thai visa policies, every 30 days Mr Day is required to leave the country and return to receive a renewed visitors visa.

He returned from an overnight stay in Cambodia this week and if the girls are not returned within next 30 days, he will face a three or four day trip to Laos.

Charlotte added: “Despite requests to the embassies we have received no assistance with regard to Rob being granted an open-ended visa to enable him to stay in Thailand to continue the search.

“Both of the girls have missed so much - the last few weeks of school, especially important for Annie as she is due to start her new secondary school in September and she missed the leavers service and end of term celebrations, sports day which they both would have loved taking part in.”

Ananya would have celebrated her 11th birthday seven weeks after disappearing, and the family are growing increasingly concerned for the welfare of the girls.

Charlotte said: “As a family we can’t imagine what Ananya and Aleena are going through. They have been taken away from their father who has looked after them from day one and they have not been allowed any contact with their family and friends in the UK. We are praying for their safe return as quickly as possible.”

The Sundridge and Brasted C of E Primary School pupils were born in Thailand but have been living in Chipstead with their father and Grandparents, Betty and Gordon since the split.