A group of United Nations experts on Wednesday voiced concern about the Spanish trial of top judge Baltasar Garzon, accused of abuse of power in probing Franco-era crimes.

"It is regrettable that Judge Garzon could be punished for opening an investigation which is in line with Spain's obligations to investigate human rights violations in accordance with international law principles," said Gabriela Knaul, UN Special Rapporteur on the independence of judges and lawyers.

The view was echoed by five independent experts of the UN working group on enforced or involuntary disappearances.

Garzon is being prosecuted for ordering an investigation in 2008 into the disappearance of 114,000 people during Spain's 1936-39 civil war and General Francisco Franco's subsequent dictatorship.

The judge argues that the acts were crimes against humanity and therefore not subject to an amnesty that had been agreed by Spain's main political parties after Franco's death.

"In the context of full respect for the independence and autonomy of the judiciary, supposed errors in judicial decisions should not be a reason for the removal of a judge and, even less, for a criminal proceeding to be launched," said Knaul.

The working group said that an amnesty law should not allow an end to a state's obligation to investigate and prosecute those responsible for disappearances.

Garzon was suspended from his duties at the National Court, Spain's top criminal court, in May 2010. If convicted he would not go to prison but could be suspended from the legal profession for up to 20 years.