KOSOVSKA MITROVICA (AFP) - The father of a 15-year-old Roma girl whose detention during a school trip and subsequent deportation to Kosovo has shaken France, vowed on Friday to take his family back to their adopted country, illegally if necessary.

"If the (French) authorities do not let me return to France legally, I will go through the forests," 47-year-old Resat Dibrani said.

Meanwhile, thousands of students protested across France and shut schools to voice their anger at the high-profile expulsion of his daughter Leonarda Dibrani earlier this month, in a case that has sparked a national uproar and raised questions about the government's immigration policy.

Much of the criticism has focused on how the girl was forced to get off a bus full of classmates on October 9 in the midst of a school outing before she was deported with the rest of her family to Kosovo.

In the latest twist in the saga, Leonarda's father on Thursday admitted lying about his family's Kosovo's origins to boost their chances at winning asylum in France.

Mr Dibrani now says he is the only one in his family to have been born in the breakaway province which declared independence from Serbia in 2008.

His wife Xhemaili, 41, was born in Italy as well as five of their six children, including Leonarda.

He took his family to France from Italy in 2008 "without papers", he said on Friday.

"I burnt my and my wife's residence permit in Italy and I told French authorities that we were all from Kosovo when we applied for asylum."

Mr Dibrani said he had decided to leave Italy after being told by authorities there that his children could obtain Italian citizenship only when they turned 18.

In France, they could "obtain French identity papers after 10 years," he said.

An AFP reporter visiting the family in the northern town of Mitrovica, where they have been resettled by Kosovo authorities, was shown copies of the birth certificates of all the children, including the youngest, 17-month-old Medina, the only one born in France.

To obtain documents for his asylum request in France, Mr Dibrani said he had bought a fake marriage certificate "for 50 euros (S$84.70) in Paris."

"This kind of paper you can find everywhere in Paris," he said.

Since arriving in Kosovo, Leonarda and her siblings, who do not speak Albanian, have refused to go to a local school.

"If there is a God we will be aboard the first plane back to France," Leonarda said in an interview on Thursday.