(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.
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 don'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."
CNN's Greg Botelho contributed to this report.