A top UN official says Syrians will soon overtake Afghans as the world's biggest refugee population, with their numbers topping 4 million by year's end "if current trends continue."

UN High Commissioner for Refugees Antonio Guterres offered his assessment Tuesday as the international community sharply urged Syria to comply with a new Security Council resolution demanding that President Bashar Assad and the opposition provide immediate access for humanitarian aid.

At a General Assembly meeting, the European Union warned that "deliberate denial of humanitarian aid is a war crime," and UN High Commissioner for Human Rights Navi Pillay demanded that the Syria situation be referred to the International Criminal Court.

Opposition activists say more than 140,000 have died in the conflict, which enters its fourth year next month.