( CNN ) -- At least 40 people were killed in an explosion at an ammunition depot in the embattled city of Homs , the Syrian Observatory for Human Rights said Thursday . The opposition organization cited medical sources , who told the group that the death toll may increase because of the serious injuries to survivors . There are also unaccounted for victims , the group said . The explosion occurred in the Wadi Aldahab neighborhood after several shells fell on the pro-regime quarters of the city , including Wadi Aldahab , the group said . Meanwhile , United Nations inspectors in the Netherlands are preparing to travel to Syria to investigate three reports of chemical weapons use , a spokesman said Thursday . `` The team is now assembling ( at ) The Hague and will be ready to depart once the remaining logistical and legal details of mission have been finalized , '' U.N. spokesman Martin Nesirky said . The team will consist of a head of the mission and about 10 experts from the Organisation for the Prohibition of Chemical Weapons and the World Health Organization , Nesirky said . The upcoming visit followed talks last week between Syria 's government and a U.N. representative for disarmament affairs , the U.N. said . Syria has been embroiled in a bloody civil war for more than two years , during which more than 100,000 people have been killed and millions have been displaced or become refugees in other countries , according to the United Nations . Amid the fighting , there have been numerous allegations that chemical weapons have been used . Syria : Fast Facts . In June , the White House said Syrian President Bashar al-Assad 's forces had crossed a `` red line '' by using chemical weapons , including the nerve agent sarin gas , against rebel forces . This prompted the U.S. government to begin providing military support to opposition fighters , despite its earlier reluctance to do so . Syria 's government , meanwhile , has claimed rebel fighters have used chemical weapons as well . That includes a March incident in Khan al-Asal in the northern province of Aleppo , according to state media . Opposition officials have said rebels do n't have access to chemical weapons or the missiles needed to use them in an attack , while other rebel leaders said Syrian troops fired `` chemical rockets '' at civilians and opposition forces . Nesirky said the team will investigate the Khan al-Asal incident and added that `` the locations of the two other incidents are being kept confidential as safety and security precaution . '' Read more : Syria 's president is all smiles on his new Instagram account . CNN 's Greg Botelho contributed to this report .
September : U.N. chemical weapon experts will investigate two ' confidential ' explosions in Syria . Syrian Observatory for Human Rights says the death toll may rise . The blast occurred in the Wadi Aldahab area in Homs , the group says . It says the explosion occurred after bombs fell on pro - regime parts of the city .