( CNN ) -- At least 800 people have been killed in a key Syrian city over the past 40 days , a Syrian monitoring group said Sunday . Most of those killed were ISIS militants and Syrian Kurdish fighters , battling for control of Kobani , according to the Syrian Observatory for Human Rights . The monitoring group based in London broke down the casualty figures starting September 16 , the day ISIS began its attack on the Syrian Kurdish enclave . More than half of the 815 people killed -- 481 -- were fighters with ISIS , which calls itself the Islamic State , the Syrian Observatory said in a statement . They were killed in ambushes and suicide car bombings as well as in attacks led by a Kurdish female commander , the group said . The group said 302 Syrian Kurdish fighters were also killed . Two civilians beheaded . Civilians accounted for 21 of the dead ; two of them were beheaded , according to the statement . The real death toll could be a lot higher . The group said it believes the actual casualty figure is twice the number documented , `` because there is absolute secrecy on casualties and due to the difficulty of access to many areas and villages that have witnessed violent clashes and bombardment by the two sides . '' Video from Kobani on Sunday showed a plume of smoke rising above the city , known in Arabic as Ayn al-Arab . Most of the city 's 200,000 people have fled across the border into neighboring Turkey . New York Times : ISIS hostages were tortured before beheadings . U.S. military strikes . Word of the casualties comes as U.S. military forces continue to strike ISIS targets in Syria . The U.S. military has conducted five airstrikes near Kobani since Saturday , according to a statement released by U.S. Central Command on Sunday . Separately , the United States and its allies have conducted some 12 airstrikes in Iraq since Saturday , according to the CENTCOM statement .
481 of those killed were ISIS fighters , according to the Syrian Observatory . 302 Syrian Kurdish fighters also died in battles with ISIS , group says . Comment: