The Syrian government has sent U.N. investigators the results of blood and soil testing from a mysterious attack that killed 25 people and injured more than 110 others , CNN affiliate ITN reported Sunday . Syria has claimed that rebels used chemical weapons in an attack Tuesday in Khan al-Asal in the northern province of Aleppo , according to state-run media . Opposition officials have said rebels do n't have access to chemical weapons or the missiles needed to use them in an attack . Other rebel leaders have claimed Syrian troops fired `` chemical rockets '' at civilians and opposition forces . Syrian opposition leader steps down ; Israeli troops face fire from Syria . U.S. President Barack Obama and other American officials have said in recent days there was no intelligence to substantiate reports that rebels used chemical weapons against government troops . And a U.S. military official directly familiar with preliminary intelligence analysis of the attack told CNN there were `` strong indications '' that no chemical weapon was used . The United States , in part , looked at video of the victims released by state-run television . Analysts believe it 's possible people in the video were deliberately exposed to a caustic agent such as chlorine , the official said . But that would not be the same as using chemical weapons such as a nerve or blister agent . Syrian refugees flood Jordanian town . Sunday , ITN reported three unnamed Syrian medical or military officials said Damascus believes a small amount of chlorine mixed with saline and a homemade rocket were used . `` All sources we have spoken to say there is a pattern of victims suffering a variety of respiratory complaints from mild breathing difficulty , through fainting and vomiting to loss of consciousness and death , '' reporter Alex Thomson wrote on his blog . `` In most cases there were no signs of any conventional blast injuries in terms of external lacerations , burns or fractures , they say . '' Victims ' blood samples , soil samples and rocket debris were sent to the United Nations , he reported . Thomson wrote that the sources said the rocket was fired from an area that has been controlled by the radical Islamist group al-Nusra Front for `` some time . '' The group is one of the most effective in the Syrian resistance , drawing on foreign fighters with combat experience in Iraq and elsewhere . In December , the U.S. State Department moved to blacklist the rebel group as a foreign terror organization linked to al Qaeda in Iraq . The Syrian government last week sent a written request to the U.N. for an investigation . The United Kingdom and France also put in requests . Jean Pascal Zanders , a chemical weapons expert and a senior research fellow for the European Union Institute for Security Studies , cast doubt on the use of chlorine , saying in an e-mail that one small rocket could n't deliver the quantity needed to kill 25 people . Chlorine is n't listed on any of the three lists of chemicals banned by the Chemical Weapons Convention of 1997 . `` It is no longer considered effective as a warfare agent , `` he wrote . Official : 'Something went down ' in Syria , but it was short of chemical weapons . Thomson added that in war , both sides lie , but this `` is the most detailed account yet of what the Syrians believe happened . '' Analysts believe the Syrian government may have one of the largest stockpiles of chemical weapons in the world . Specifically , the supply is believed to include sarin , mustard and VX gases , which are banned under international law . Syria has denied the allegation . The Chemical Weapons Convention prohibits the production , stockpiling and use of chemical and biological weapons . Syria is not one of the 188 signatories to the convention . In recent months , reports have repeatedly surfaced that Syrian forces moved some of the chemical weapons inventories , possibly because of deteriorating security in the country , raising fears the stockpile could fall into the hands of al Qaeda-linked groups working with the opposition should Syrian President Bashar al-Assad 's government fall . Focus on Syria : Chemical weapons frightful , relatively inexpensive .
Expert doubts one rocket could carry enough chlorine to kill dozens . CNN affiliate reports results of blood and soil testing sent to United Nations . Sources tell ITN that chlorine mixed with saline was used in attack . Rebels have said they have no access to chemical weapons .