A panel of top judges in Spain says the country's courts have no jurisdiction to investigate the first foreign criminal case for torture and terrorism against the Syrian government.

The U-turn by Spain's National Court is a setback for activists and human rights campaigners who had hailed the case as a stepping stone for accountability in Syria.

Judge Eloy Velasco was investigating the alleged role of nine Syrian intelligence and security officials — including long-time Vice President Farouk al-Sharaa, intelligence chief Ali Mamluc and air force intelligence chief Jamil Hassan — in the disappearance and killing of a man in 2013.

The body of Abdulmuemen Alhaj Hamdo emerged among the trove of macabre photographs smuggled out of Damascus by a sympathetic forensic photographer codenamed Caesar.

The man's sister, Amal Hag Hamdo Anfalis, a Spanish national, filed the complaint in February with the support of Guernica 37, a group of international lawyers.

On Friday, the court decided to drop the probe after the public prosecutor argued it lacked jurisdiction to judge the crimes, a court statement said.

Maite Parejo, one of the plaintiff's attorneys, said that lawyers with G37 were still waiting for the court's documents but that the firm planned to study legal actions to re-open the probe by appealing before Spain's Supreme court.

The Syrian civil war, now in its seventh year, has killed some 475,000 people, including around 100,000 civilians, according to the Britain-based Syrian Observatory for Human Rights.

Spain has previously taken up universal justice cases against foreign nationals although almost none has concluded in trial.