A group of four investigators led by Paulo Pinheiro of Brazil issued a 121-page report to the Human Rights Council saying conditions for civilians in Syria are deteriorating rapidly, "aggravated by increased sectarianism."
Meanwhile, the European Council's Foreign Affairs Council in Brussels voted to extend its sanctions against Syria.
The U.N. investigators said they found credible evidence of human-rights abuses and war crimes committed by both the Bashar Assad-led government and opposition forces, The New York Times reported
"Indiscriminate and widespread shelling, the regular bombardment of cities, mass killing, indiscriminate firing on civilian targets, firing on civilian gatherings and a protracted campaign of shelling and sniping on civilian areas have characterized the conduct of the government," the report said.
The panel compiled a list of names of leaders who may be responsible for carrying out the abuses and called for stronger action by the international community to act on their findings.
"The issue of accountability for those responsible for international crimes deserves to be raised in a more robust manner to counter the pervasive sense of impunity in the country," the report said.
Referral to the ICC can only come from the U.N. Security Council. Russia and China have vetoed the move, saying it's prejudicial to the survival of the Assad government, the Times reported.
EU High Representative Catherine Ashton said in a statement posted on the EU's website the council reaffirmed its position that the violence in Syria "remains totally unacceptable."
"We were all encouraged by the recent initiative by the coalition leader Sheik Moaz al-Khatib for a political dialogue," Ashton said. "We hope that representatives of Syrian regime do not miss this opportunity to help end the violence.
"Today we also agreed to extend sanctions against Syria for a further three months and we are amending them so as to enable greater non-lethal support and technical assistance for the protection of civilians.
"We will of course continue to assess and review the sanctions regime, if necessary, to support and help the opposition and to ensure that we are providing the best we can for the people on the ground," she said.