The Government of Cyprus has said it has “full confidence in the justice system and the courts” after a British teenager was found guilty of lying about being gang-raped.

The Foreign Office said the UK was “seriously concerned” about the fairness of the 19-year-old woman’s trial and it is understood officials have raised the “deeply distressing case” with the Cypriot authorities.

Lawyers and campaigners criticised the justice system after she was convicted of public mischief at Famagusta District Court, in Paralimni, on Monday.

And the psychologist who assessed the woman as part of her defence case, Dr Christine Tizzard, said she was concerned the trial had not fully considered that she had been diagnosed with post-traumatic stress disorder (PTSD).

She told the Guardian: “The salient point is that she was diagnosed with PTSD. That’s a standalone diagnosis. It’s a valid diagnosis and it hasn’t really been fully represented.

“Aside the fact it hasn’t been fully represented, it means she’s been unable to get the treatment she so sorely needs and every day she’s not having treatment the worse it gets.”

But a Cypriot government spokesman said: “The Republic of Cyprus as an orderly state has constitutionally established institutions and separation of powers.

“In this context, the government does not intervene in cases brought before the competent courts of the Republic of Cyprus, nor does it comment on positions or allegations which are raised with respect to cases still pending before the courts.

“The government has full confidence in the justice system and the courts of the Republic of Cyprus, which should be left unfettered to implement state laws and deliver justice.”

The teenager said she was raped by up to 12 Israeli tourists in a hotel room in the party town of Ayia Napa on July 17.

But she was charged and the dozen young men, aged between 15 and 20, who were arrested over the incident, were freed after she signed a retraction statement 10 days later.

The woman, who had been due to go to university in September, claimed in court she was raped but forced to change her account under pressure from Cypriot police.

Judge Michalis Papathanasiou said he believed the woman had made false allegations because she felt “embarrassed” after realising she had been filmed having sex in a video found on some of the Israelis’ mobile phones.

“The defendant gave police a false rape claim, while having full knowledge that this was a lie,” he said.

“There was no rape, or violence, and police had carried out a thorough investigation making all necessary arrests.”

The woman has been on bail since the end of August, after spending a month in prison, and could face up to a year in jail and a 1,700 euro (£1,500) fine when she is sentenced on January 7.

Her lawyers said they will appeal against the verdict in the Supreme Court of Cyprus and the European Court of Human Rights if necessary.

The teenager said that she was “dedicated to seeking true justice”, while her mother described the verdict as “absolutely astonishing” and said her daughter was “effectively in a gilded cage” as she awaits sentencing on the island.

Speaking to The Sun, the woman said she was not surprised by the verdict.

“We expected this almost from the very start,” she said. “One moment I was the victim, the next, I was the accused.

“Eight hours of interrogation, denied access to a lawyer – while those accused of raping me had legal representation immediately.”

A Foreign Office spokesman said: “The UK is seriously concerned about the fair trial guarantees in this deeply distressing case and we will be raising the issue with the Cypriot authorities.”