"But when I see people using awful, terrible chemical weapons-which they agreed not to use under the Obama administration, but they violated it". We have stated our position on many occasions. "And I, for one, am really, really wary and anxious about getting committed to another land war and making the same mistake that we did in Iraq". He added that Mr Assad had presided over more than 50 attacks, using weapons such as cluster bombs and chlorine bombs "intended to main and kill in the most horrific ways".
The news conference came after Russian President Vladimir Putin met the top American diplomat for nearly two hours to see if they could rescue relations between the world's mightiest military powers.
Tillerson said the United States was confident that Assad's forces were behind the gas attack, but said there was "no firm information" to indicate Russian forces were involved in the same attack.
Mr Tillerson reiterated the USA position that Syrian President Bashar al-Assad must eventually relinquish power in Syria, a position starkly at odds with Russian Federation.
"I look forward to a very open, candid, frank exchange so that we can better define the US-Russian relationship from this point forward", he told Lavrov.
Ja'afari said the West and some regional countries provide the terrorists fighting in Syria with chemical weapons.
U.S. Intelligence agencies have tried to accuse Putin of trying to help Trump during the presidential elections.
Russia's deputy United Nations envoy, Vladimir Safronkov, said the draft resolution laid blame prior to an independent investigation.
Before the vote, Russia's deputy United Nations envoy Vladimir Safronkov said in the course of negotiations between his country's Foreign Minister Sergey Lavrov and US Secretary of State Rex Tillerson, Moscow had suggested a joint communication asking the OPCW Director-General to immediately put together an worldwide mission to visit Khan Shaykhun and the Shayrat air base.
The meeting took place along with Lavrov and came after Lavrov issued Tillerson a warning against any further USA strikes on the Syrian regime. "This council should not just say it's for a political solution, but also actively pressure the parties to prove it. that means adopting resolutions that say what we mean, resolutions that we are all willing to uphold".
Earlier, Tillerson said relations between Moscow and Washington are "at a low point" and marked by serious distrust.
The US Secretary of State was considering that proposal, he said, adding that the whole gamut of issues would be discussed by OPCW on April 13 at The Hague.
He said working groups would be established to improve U.S.
Rycroft said Russian Federation has a choice of sticking with "the toxic Assad regime that poisons its own people" or seeking peace through negotiations and a political transition.
The Kremlin had previously declined to confirm Putin would meet Tillerson, reflecting the renewed tension.
Still, Tillerson sought to stress the positives from his meetings. Until the chemical attack, the Trump administration had sought to step back from the US position that Assad should leave power.