"We don't have arsenal".
World leaders, including President Trump, immediately accused Assad of using chemical weapons against his own people, again, in violation of worldwide accords.
Samples taken from Khan Sheikhoun last week tested positive for the nerve agent sarin, the British delegation t the global chemical weapons watchdog OPCW said on Thursday.
Over 80 people died in the April 4 Khan Shaykhun purported gas attack, which Western countries blamed on the Syrian government.
U.S. Ambassador Ward insisted it was a deliberate attack that amounted to "a direct affront to the Chemical Weapons Convention and, indeed, a direct affront to human decency, carried out by a State Party" to the OPCW, according to the text of his speech that was posted on the organization's website. "That is our position on the use of chemical weapons", he said.
Trump's administration initially took a hands-off approach to Syria, with Assad raising the possibility the new United States president could even be a "natural ally". The Britain-based Syrian Observatory for Human Rights monitoring group reported 25 SDF fighters were killed in the last two days of battle, while the activist-run Raqqa is Being Slaughtered Silently group said on Wednesday that three days of mourning were to be held in a border town held by the SDF after the arrival of the bodies of 15 fighters from the battle.
The Khan Sheikhun incident prompted the first direct United States military action against Assad's government since the war began, with 59 cruise missiles hitting the Shayrat airbase three days after the suspected chemical attack. Their timing and location have been verified by independent researchers. Brig. Gen. Zaher al-Sakat, a general who said he defected from Assad's army, told CNN's Christiane Amanpour in 2013 that Assad would not give up the chemical weapon stockpile.
"Apart from anything else, we believe it's only the regime that has the capability to make such an attack".
Turkey, which treated numerous wounded, says it has "concrete evidence" Sarin was used.
France, Britain and the United States pushed for a tough investigation and demanded that Syria provide information on its military operations, but that proposed draft faced the likelihood of a veto from Russian Federation.
Assad denied having chemical weapons and said Syria would only allow an "impartial" investigation into the incident.
US -backed Syrian Kurdish forces say they have entered the fourth stage of their campaign to capture the Islamic State group's de facto capital Raqqa with an advance on the militants in a valley north of the city.
The US had, until its Shayrat attack, limited its involvement in Syria to removing the so-called Islamic State (IS) from its stronghold in the city of Raqqa.
A spokesman for the US military coalition that operates bombing missions against the Islamic State in Syria denied the report.
Trump gave such criticism short shrift on Wednesday, saying: "I felt we had to do something about it".