The findings supported earlier testing by Turkish and British laboratories.
After the US strike, Russian Federation said it would suspend its participation in a hotline with the United States military to "deconflict" or minimize the risk of mid-air collisions in Syrian airspace, but USA officials said this week that the two militaries continued to communicate.
Samples from seven individuals undergoing treatment at hospitals yielded similar results, Uzumcu said.
Assad said in an interview with the Russian state-owned RIA Novosti news agency on Thursday that the U.N. has not sent anyone yet and blamed Western nations and the United States in particular for not allowing the experts to travel to Syria.
Mr Assad claims the poison gas attack is a fabrication used to justify the U.S. air strike.
Israel said it believed Syria retained up to three tonnes of the weapons.More news: Secret Service limits sidewalk access south of White House
The attack this month in the rebel-held town of Khan Sheikhoun killed 86 people.
Brigadier-General Zaher al-Sakat, who served as the head of chemical warfare in a top Syrian military unit before defecting in 2013, said that Assad had not declared large amounts of sarin and its precursor chemicals. It was the first time U.S. forces had directly attacked government forces in the six-year civil war. The fighting has killed an estimated 400,000 people and displaced half of Syria's population.
"The Syrian regime should think long and hard before it again acts so recklessly in violation of global law against the use of chemical weapons", Mattis said, later adding: "If they use chemical weapons, they are going to pay a very, very stiff price".
The missile strike was the first direct United States military action against Assad's forces since the start of Syria's civil war six years ago and precipitated a downward spiral in ties between Washington and Moscow. During the six-year conflict, Israel has largely stayed on the sidelines, carrying out occasional air strikes against what it says is the movement of weapons to Iranian-backed Lebanese Hezbollah militants.
Syrian President Bashar al-Assad circumvented a 2013 deal to dismantle his chemical weapons stockpile by failing to declare the full extent of his arsenal, Syria's former chemical weapons research chief told The Telegraph on Saturday.
The French foreign minister said his Government was preparing to publish evidence to show the Syrian Government knowingly used chemical weapons in the incident.