When Russian and Syrian warplanes pummeled civilian infrastructure in Idlib province, they did so without warning or a legitimate military target, Human Rights Watch said in a new report calling on world governments to hold President Vladimir Putin and other high-ranking Russian officials responsible for failing to prevent war crimes and possible crimes against humanity in Syria.

The New York-based watchdog described what it said were deliberate and disproportionate attacks on civilians carried out by the Syrian government and its ally Russia during their 11-month offensive to retake Idlib, the last major swath of territory still in the hands of the opposition after nearly a decade of war. 

By the time Turkey and Russia announced a cease-fire in March, the fighting had left at least 1,600 civilians dead, the United Nations estimates. The regime's offensive also forced some 1.4 million people to flee their homes, with many finding refuge in crowded camps along the closed Turkish border. 

Human Rights Watch examined 46 air and ground attacks carried out by the Syrian-Russian alliance on civilian objects and infrastructure, including schools, hospitals and markets. The attacks represent just a fraction of the total use of cluster munitions, incendiary weapons and improvised barrel bombs used in Idlib, the group said.