Geneva - Syrian government forces have dropped barrel bombs on Aleppo nearly daily this year, amounting to the war crime of targeting civilians, and insurgent shelling has caused mass casualties, UN investigators said on Tuesday.The military and rebel groups, including Islamic State, have imposed sieges to "devastating effect" on a total of 420 000 Syrians, depriving them of food and medicine and leading to malnutrition and starvation, they said."Civilians continue to lose their lives, homes and livelihoods in a conflict in which there little if any attempt to adhere to international law," Paulo Pinheiro, chairman of the U. commission of inquiry, told a news conference.More than 220 000 people have been killed in the four-year conflict that has driven 4 million refugees abroad.This year, government planes and helicopters have bombarded areas of eastern Aleppo province, "mostly barrel bombings - on a nearly daily basis," the independent experts said in their latest report to the UN Human Rights Council. Government bombing of towns and cities in Deraa and Idlib also intensified."The continuing use of barrel bombs in aerial campaigns against whole areas, rather than specific targets, is in violation of international humanitarian law and, as previously documented, amounts to the war crime of targeting civilians," the report said.The investigators warned: "The flight paths of helicopters responsible for the dropping of barrel bombs are being documented. Those in command of the bases and airstrips where helicopters are loaded and from where they take off must be held accountable."Vitit Muntarbhorn, a Thai expert on the commission, told reporters that its five confidential lists of suspected war criminals had been merged into a single one."Now five lists have been consolidated into one, synchronised with all the details. It remains confidential for now."Syrian Ambassador Hussam Eddin Aala rejected the inquiry's findings about government practices, adding:"The terrorist group ISIS has committed massacres in Palmyra and caused deaths and injury of hundreds of people, however these crimes don't seem to have found their way into the report."Aala accused the UN investigators of "collusion and bias" for failing to denounce Turkey, Saudi Arabia and Qatar for supporting rebels fighting to topple President Bashar al-Assad.Pinheiro declined to name states providing all sides with what he called "more weapons, more money, more combatants"."At the same time those who bear the greatest responsibility for the crimes, violations and abuse against Syrians fear no consequences. It's a feast of impunity, this conflict in Syria."