Foreign ministers from the European Union insisted Wednesday that they would demand "accountability" from Syria's Bashar Assad regime, as well as extremist and other armed groups, over the alleged war crimes committed since the 2011 uprising that plunged the country into civil war.

"Our countries are committed to ensuring that war criminals and torturers will not go unpunished," the 18 ministers said in a joint statement published on the website of the French Foreign Ministry.

In the past 10 years, nearly 400,000 people have been killed and more than 6 million have been forced to flee the country to escape "countless violations of human rights," the ministers said.

Bashar Assad, who is backed by Russia, has also been accused of using chemical weapons in breach of international law as he regained 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.

The statement comes after international donors on Tuesday pledged $6.4 billion in aid for Syria and the thousands of refugees in neighboring countries, missing the $10 billion target set by the United Nations.

The need for aid has increased on the back of 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 fueled the rise of the Daesh terrorist group.

European countries insist they will not spend money on a broader rebuilding in Syria until Assad commits to a genuine political process to resolve the conflict.