EU foreign ministers on Wednesday said they would demand "accountability" from Syria's government and militias over any crimes committed since the 2011 uprising plunged the nation into civil war.
"Our countries are committed to ensuring that war criminals and torturers will not go unpunished," the 18 ministers said on the French Foreign Ministry website.
In the past 10 years nearly 400,000 people have been killed and more than six million have been forced to flee the country to escape "countless violations of human rights", the ministers said.
Syrian President Bashar Al Assad has also been accused of using chemical weapons in breach of international law as he retook control of the country.
"Full light must be shed on this decade of atrocities," the ministers said.
"We continue to call for the International Criminal Court to be allowed to investigate crimes alleged to be committed in Syria and prosecute the perpetrators."
Cases have already been filed in several European countries on the principle of universal jurisdiction, which allows suspects to be tried outside the territory of where the crimes were committed.
A German court in February convicted a former Syrian intelligence service agent for complicity in crimes against humanity, in the first such court case worldwide.
International donors on Tuesday pledged $6.4 billion in aid for Syria and Syrian refugees in neighbouring countries, missing the $10bn target urged by the UN.
The need for aid has increased after the coronavirus pandemic and a slump in the value of the Syrian pound, which has sent food prices soaring.
Efforts have stalled to find a lasting peace deal to end a conflict that has pitched world powers against each other and fuelled the rise of the ISIS.
European countries insist they will not spend money on a broader rebuilding in Syria until Mr Al Assad commits to a genuine process to resolve the conflict.