A group of lawyers in Germany is planning to launch a case against Bashar al-Assad for war crimes committed by his forces and foreign allies in the Syrian province of Aleppo.

The lawyers on Monday presented a criminal complaint against Assad, which they are submitting to German federal prosecutors.

German law allows international prosecutions on the principle of "universal jurisdiction", under which countries can pursue foreigners for crimes committed abroad.

The lawyers cited reports from the human rights organization Amnesty International and individual accounts by asylum seekers in Germany in arguing there is overwhelming evidence of multiple atrocities committed by Assad's forces against civilians in Aleppo between April and November.

"We're experiencing genocide in Aleppo in slow motion," German attorney Mehmet Daimaguler said.

He cited the targeted bombing of hospitals, cluster bombs used on civilians, and forced expulsion.

UN human rights chief Zeid Ra'ad said in October the regime's siege and bombings of of east Aleppo constituted "crimes of historic proportions", which have caused heavy civilian casualties amounting to war crimes.

He also said the case should be referred to the International Criminal Court.

The prosecution bid came as Syrian revolution forces who had controlled all of the east of the key northern city Aleppo lost a substantial portion of their territory to a major regime offensive backed by Russian air strikes and foreign fighters.

The regime's push - backed by thousands of Shia militia fighters from Lebanon, Iraq, and Iran, and under the occasional cover of the Russian air force - has laid waste to Aleppo's east.

Thousands of residents have fled to regime and Kurdish-controlled areas of the city.

PHOTO CAPTION

People inspect the damage at the Medecins Sans Frontieres (MSF)-backed al-Quds hospital after it was hit by airstrikes, in Aleppo, April 28, 2016. REUTERS

Al-Jazeera