Indiscriminate attacks and sieges of populated areas by pro-government forces in the Syrian conflict "are leading to mass casualties, malnutrition and starvation," an independent U.N. panel says in a report released Wednesday.

"More than 250,000 people are besieged in the Syrian Arab Republic and subjected to relentless shelling and bombardment. They are denied humanitarian aid, food and such basic necessities as medical care, and must choose between surrender and starvation," the members of the U.N. Commission of Inquiry said.

The Commission's seventh report on Syria is based on information gathered between June 15, 2013, and Jan. 14, including 563 interviews conducted with war refugees.

The panel found that both forces loyal to President Bashar Assad and opposition fighters have committed massacres.

"Among the most devastating events we documented was the campaign of barrel bombing in Aleppo targeting entire areas and spreading terror among civilians," the Commission chairman, Paulo Sergio Pinheiro, said at a press conference in Geneva.

"There is an increase in child recruitment among several non-state armed groups. Children are not only involved in the armed conflict, but they have been targeted by snipers. The Syrians we met a few days ago fell abandoned and hopeless," he said.

"The absolute impunity that pervades the conflict, now entering its fourth year, is utterly unacceptable. The leadership of each party must be held responsible for the violations of its members," Pinheiro said.

He and his colleagues on the Commission also blamed the U.N. Security Council - led by permanent members the United States, Russia, China, Britain and France - for failing to end the impunity.

The Security Council's inaction "has provided the space for the proliferation of actors in Syria, each pursuing its own agenda and contributing to the radicalization and escalation of violence," the Commission said.

Without mentioning any country by name, the Commission sought to warn backers of the respective sides about their own potential culpability.

"External actors that support the belligerents financially and logistically have obligations under international law," the report said.

The war in Syria has left more than 140,000 dead and displaced some 9 million people, including 2.5 million who have fled to neighboring countries. EFE