THE UN special envoy for the Syria crisis, Staffan de Mistura, has begun a round of consultations in Geneva in the hope of finding enough common ground to launch another peace initiative. But groups involved in the war in Syria say they will not co-operate with the UN mission, amid signs of an intensification of fighting in several parts of the country.

The northern city of Aleppo, which remained mostly quiet during the opening months of the uprising against the Bashar al-Assad regime, has, for several months, found itself caught up in some of the most violent battles between government and rebel forces.

In a report just published, Death Everywhere, Amnesty International says that, in 2014 and the first three months of this year, "government forces and many non-state armed groups committed serious human rights abuses and violations of international humanitarian law in Aleppo city and its closest suburbs," some of which "appear to constitute war crimes. In some cases, the actions of the Syrian government may have amounted to crimes against humanity."

In February, the Syrian President Bashar al-Assad denied that forces loyal to his government had used barrel bombs in Aleppo or elsewhere. But Amnesty says: "Barrel bombs and other air attacks have killed, injured, and displaced tens of thousands of civilians in Aleppo and across Syria."

The organisation has documented and received reports on hundreds of incidents in Aleppo, from January 2014 to March this year, involving air strikes on "civilian objects and populated areas, including at least three schools, 17 hospitals, 12 transportation hubs, 14 public markets, and 23 mosques". Residents as well as monitoring groups told Amnesty International that barrel bombs were used in the majority of these attacks.

"The massive destruction and casualties caused, as well as the clearly identifiable remnants of barrel bombs, have been captured in thousands of videos and photos from monitoring groups, media sources, and witnesses."

The air strikes have put hospitals at risk, forcing staff to move their facilities underground. Amnesty quotes a doctor working at a field hospital in the al-Sakhour neighbourhood of Aleppo as saying: "There is no sun, no fresh air; we can't go upstairs, and there are always airplanes and helicopters in the sky. Some hospitals are above the ground, but they face huge risks." Many schools in opposition-held areas of Aleppo city have also moved into basements or underground bunkers to avoid being bombed.

As a backdrop to these grave violations, the Amnesty report says, citizens of Aleppo city "live in appalling conditions. Residents in both opposition-held and government-held areas lack basic services such as water and electricity, and suffer shortages in food, medicine, and gas to heat their homes."

Humanitarian workers told Amnesty International that they were generally able to reach government-controlled areas of the city. Yet those providing assistance to opposition-controlled districts spoke of "significant challenges to providing aid, not least of which is the government forces' continual targeting of the road that serves as the primary access route for humanitarian assistance to the city".

Amnesty International calls on "all parties to the Syrian conflict to end deliberate attacks on civilians and civilian objects such as hospitals and schools; to end the indiscriminate use of explosive weapons such as barrel bombs and mortars in populated areas; to end arbitrary arrests, enforced disappearances, abduction and torture, and other ill treatment; and to allow unimpeded humanitarian access to the UN and its implementing partners in Aleppo and in Syria as a whole".

Ultimately, the report says, the success of initiatives to secure a freeze in hostilities to allow humanitarian access "should be measured by the commitment of all warring parties to halt the human-rights abuses, war crimes, and crimes against humanity that are being committed in Aleppo and across Syria".