(CNN) -- 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 don'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.
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.
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 couldn't deliver the quantity needed to kill 25 people.
Chlorine isn'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.
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.
CNN's Salma Abdelaziz and Amir Ahmed contributed to this report.