Pop star Ariana Grande has hit out at P&O Ferries after her dogs were prevented from entering the UK.

The US singer, 21, who was making the crossing from Calais to Dover on her tour bus after performing in Amsterdam, vented her fury on Twitter over the way Toulouse and Sirius were treated.

Her mother Joan was the first to complain in a series of tweets and a long explanation in which she accused officials in Calais of being "tyrants".

"The P&O Ferry was lovely, just to set things straight, the people at the ferry border were horrible to me and to Toulouse and Sirius," she wrote.

Joan, who was later reunited with the dogs in London, complained that she had been prevented from getting on to the ferry for "no reason and against my will".

"I begged him to let me go through, he laughed at me and said no again... I kept telling him and showing him again that the dogs were fully vaccinated and were 100% vaccinated in order to enter the UK and then, I screamed!!!," she wrote.

"I had done every ridiculous task he demanded of me... and at this point he said he would call the police and have me arrested if I tried to go through... I told him to call them and to arrest me, because that was the only way I was not getting on the ferry."

She said that after running back on to the tour bus with the dogs, "suddenly, the bus driver appeared and said that there were men outside the bus to arrest me".

"I collected myself, took a deep breath and ran out yelling: 'Take me away with the dogs and I will sue you for abuse and harassment'... I told them that they were wrong, they were targeting Americans, they were abusing their authority... they laughed....

"At this point, one man in a yellow jacket said to me, 'If you take the dogs, when you arrive in Dover, they will be killed!' ... I actually thought I disengaged from my body as tears started streaming down my face, and I felt as if I were losing my mind!!! I told him that they would have to kill me first and we would see what the US embassy would say about that."

Her daughter later wrote on Twitter: "This was unacceptable. @poferries please have your employees treat people /animals with respect. Kindness goes a long way."

Mother and daughter were later reunited with the pets after the animals were assessed by a vet in the French town of Calais.

"The pups were safe and sound thanks to (half-brother) Frankie but it was indeed a terrible experience. No animal / human should be treated that way... ever," the pop star said.

A spokesman for P&O Ferries said: "We completely understand and sympathise with Ms Grande's frustration, given her attempts to do the right thing.

"However, the documents she presented were not valid to bring her pets into the UK.

"There are only two documents we can accept. One is a Pet Passport, the other is a Third Country Veterinary Certificate. The appropriate verification of treatments must be written into these documents.

"That's why we had no alternative: we had to advise that a local vet should be visited to put everything in order. We carry in the region of 40,000 pets a year between Calais and Dover as a matter of routine. However from time to time we have to decline to carry pets due to irregularities with the documentation stipulated by Defra."