JERUSALEM ( CNN ) -- The international group Human Rights Watch is accusing Israel of firing weapons containing white phosphorus into Gaza . The group demands that the alleged practice cease . Israel is declining to say whether bursts like this over Gaza involve white phosphorus . The group 's researchers in Israel `` observed multiple air-bursts of artillery-fired white phosphorus over what appeared to be the Gaza City/Jabaliya area '' on Friday and Saturday , the organization said on its Web site . `` Israel appeared to be using white phosphorus as an 'obscurant ' [ a chemical used to hide military operations ] , a permissible use in principle '' under the laws of war , the HRW posting said . `` However , white phosphorus has a significant , incidental , incendiary effect that can severely burn people and set structures , fields , and other civilian objects in the vicinity on fire , '' the posting said . `` The potential for harm to civilians is magnified by Gaza 's high population density , among the highest in the world . '' HRW said the use of white phosphorus in Gaza would violate `` the requirement under international humanitarian law to take all feasible precautions to avoid civilian injury and loss of life . '' Last week , an Israel Defense Forces spokesman told CNN : `` I can tell you with certainty that white phosphorus is absolutely not being used . '' Now , however , Israeli officials have a different response to questions about the possible use of phosphorus : `` Any munitions that Israel is using are in accordance with international law . Israel does not specify the types of munitions or the types of operations it is conducting . '' Still , a doctor familiar with the material said it is not possible to tell , based on pictures of burns , whether white phosphorus was responsible . `` Dead tissue pretty much looks the same , '' said Dr. Peter Grossman , president of the Grossman Burn Center in Sherman Oaks , California . The chemical `` can burn down houses and cause horrific burns when it touches the skin , '' said Marc Garlasco , senior military analyst at Human Rights Watch . Since January 3 , when Israel began its ground offensive in Gaza , news reports have circulated about the possible use of white phosphorus by the IDF . HRW 's assertion was supported by munitions experts and some Palestinian doctors , including Nafiz Abu Sha'aban , who said the burns it caused were unlike anything he has seen in 27 years of practice . Watch footage of burn patients in Gaza . Though most severely burned patients have been sent to Egypt , the ongoing fighting has made it impossible to evacuate all of them , including one man with deep burns over 47 percent of his body , the doctor said . White phosphorus is known to burn flesh down to the bone . It 's intended to provide illumination or to create a smokescreen in battle . Under an international protocol ratified by Israel in 1995 , the use of such incendiary weapons is allowed when `` not specifically designed to cause burn injury to persons . '' There is no prohibition per se against white phosphorus in conflict . But the timing and location of its use are restricted . For example , it is illegal under the protocol to use white phosphorus against any personnel , civilian or military . It can be directed only against military targets . International law says incendiary weapons can not be used where civilians are concentrated . A house north of Gaza City was hit Sunday by something that observers contend may have been white phosphorus . `` It 's been burning since one o'clock in the morning , '' Munir Hammada told CNN 11 hours later . `` If you move it with your feet , it reignites . You ca n't put it out with water , only sand . '' Those characteristics match the properties of white phosphorus , which ignites on contact with air .
Researchers in Israel saw bursts of white phosphorus over Gaza , group says . White phosphorus can burn people , set structures on fire . It's not clear if the rockets were fired from inside or outside Gaza[/u] '' Group : Use in densely populated Gaza would violate international humanitarian law .