More than 27,000 images of torture and killings allegedly perpetrated by the Assad regime in Syria have been handed to German prosecutors who are investigating possible abuses, a rights group said Friday.

"The photos show the extent and the systematic nature of torture" under Syrian President Bashar al-Assad, said Wolfgang Kaleck, general secretary of the European Center for Constitutional and Human Rights (ECCHR).

The shots were taken by a photographer working for the Syrian military police, dubbed "Caesar", who fled his homeland in 2013 carrying 55,000 photographs showing bodies of people who had been tortured between 2011 and 2013.

The rights group said it had joined Caesar on Thursday in filing a criminal complaint with Germany's federal prosecutor against senior officials from the Syrian intelligence service and military police over possible crimes against humanity and war crimes.

Although the alleged abuses were carried out in Syria and not Germany, the case can be filed on German soil under the legal principle of universal jurisdiction, meaning that any country can pursue perpetrators regardless of where the crime was committed.

Germany is one of the few countries in the world to apply the principle.

In France, a similar investigation over crimes against humanity was opened two years ago on the basis of Caesar's account as a witness.

The German case was filed just months after seven individuals who claim they were tortured filed claims against the top brass of Syria's secret service.

According to Spiegel weekly, German investigators are currently examining cases against 12 leading officials of the Assad regime.