Prosecutors said Tuesday they had asked France's highest court to review the legality of a French arrest warrant for Syrian President Bashar al-Assad over deadly chemical attacks on Syrian soil in 2013.
Syrian opposition say one of those attacks in August 2013 on the rebel-held suburbs of Damascus killed around 1,400 people, including more than 400 children, in one of the many horrors of the 13-year civil war.
Prosecutors said they had made the request to the Court of Cassation on Friday on judicial grounds, two days after an appeals court upheld the arrest order.
"This decision is by no means political. It is about having a legal question resolved," the prosecutors told AFP.
France is believed to have been the first country to issue an arrest warrant for a sitting foreign head of state in November.
Investigative magistrates specialised in so-called crimes against humanity, issued the warrant after several rights groups filed a complaint against Assad for his role in the chain of command for the alleged chemical attacks in the capital's suburbs on August 4, 5 and 21, 2013.
But prosecutors from a unit specialised in investigating "terrorist" attacks have sought to annul it, although they do not question the grounds for such an arrest.
They argue that immunity for foreign heads of state should only be lifted for international prosecutions, such as at the International Criminal Court (ICC).
The Syrian Centre for Media and Freedom of Expression (SCM), lawyers' association Open Society Justice Initiative (OSJI) and the Syrian Archive, an organisation documenting human rights violations in Syria, filed the initial complaint.
SCM head Mazen Darwish was indignant.
"We view (the) filing of the appeal as a political manoeuvre aimed at protecting dictators and war criminals," he told AFP.
Lawyers Jeanne Sulzer and Clemence Witt, who are representing the plaintiffs, said the appeal to the Court of Cassation "again threatens the efforts of victims to have Bashar al-Assad judged in an independent jurisdiction".
A UN report on the August 21 attacks said there was clear evidence sarin gas was used in Moadamiyet al-Sham as well as Zamalka and Ein Tarma in the Ghouta suburbs of Damascus.
Syria's civil war has killed more than half a million people and displaced millions since it broke out in March 2011 with the Damascus authorities' brutal repression of anti-government protests.