"We are concerned they may have tampered with it with the intent of thwarting the efforts of the OPCW FactFinding Mission to conduct an effective investigation", Ward said in comments at a closed-door meeting of the OPCW in The Hague that were later made public.
Another year into Syria's war, with chemical strikes continuing, most experts suppose any new USA response must be broader, with perhaps more targets and more than one night of bombing.
A child is treated in a hospital in Douma, eastern Ghouta in Syria, after what a Syria medical relief group claims was a suspected chemical attack.
Haley, who said she would be heading to Washington for meetings later Friday, added that the National Security Council has been cautious and methodical about a decision to retaliate over the attack on the last rebel-held stronghold in Syria, which left at least 49 dead.
Two days later, the fact-finding team said it has still not been granted permission by Syrian authorities to visit Douma, the town in the Eastern Ghouta suburbs of Damascus where the attack is said to have taken place. And the three allies are considering a joint military strike in retaliation.
They agreed to "keep working closely" on the issue, Mrs May's office said in a statement. The statement said none of the patients had any symptoms of chemical poisoning. It was not immediately clear if Russian-supplied interceptors were activated.
"This is grotesque", Pierce said of the Russian statement as she left an emergency meeting of the U.N. Security Council called by Russia on US threatened military action in response to the alleged attack.
Meanwhile, the U.S. has raised concerns Russian Federation may have visited Douma and "tampered with" evidence. He didn't elaborate or name the state. A Western official told CNN that it is not conclusive, but officials suspect the substance used in the attack was a mixture of chlorine, sarin and possibly other chemicals.
Russian President Vladimir Putin is a major supporter of Syria's government.
Russia's envoy Nebenzia called on the United States, France and Britain "not to bring the world to such a unsafe threshold". Putin and Macron instructed their foreign and defense ministers to maintain close contact to "de-escalate the situation", the Kremlin said.
"Considering what has happened, we consider it possible to reassess this question and not just as far as concerns Syria, but other countries too", Rudskoi said.
USA officials have refused to rule out direct military engagement with Russian Federation, with the White House saying "all options are on the table".
Erdogan says: "What we insisted on tenaciously was the fact that is not right for tensions to heat up; we made requests concerning the restitution of peace and the end of the tragedy that is going on".
Russia's top diplomat said Friday that Moscow has proof that the suspected chemical attack in Syria last weekend was staged by special agents of a foreign country.
The group was the last in the erstwhile besieged Ghouta enclave to resist the exit proposed by Russian Federation but an alleged chemical attack by the regime on April 7 appeared to break their will.
Lavrov also said Russian specialists who examined the attack found no trace of chemical weapons.
It was "shameful" that a lack of accountability for the April 2017 attack on Khan Sheikhun "can only have reassured the Syrian regime that the global community was not serious in its stated commitment to uphold the norm against chemical weapons use", he added.
Speaking to reporters in Moscow, Lavrov reiterated a strong warning to the West against military action in Syria.
"God forbid anything adventurous will be done in Syria following the Libyan and Iraqi experience", Mr Lavrov said.
He noted that the Russian and US militaries have a hotline to prevent incidents, adding that it's not clear if it would be sufficient amid mounting tensions.
All the signs are they want to draw a line under events after the Syrian President Bashar al Assad has taken his punishment. Syria's civil war, which began as a popular uprising against Assad, is now in its eighth year.
"The sole thing that they have an interest in is to oust the Syrian government and to deter, contain the Russian Federation", he added.
A Russian defense ministry official said later the OPCW experts would travel to Douma on Wednesday.
"According to preliminary information, there were no victims among peaceful civilians and the Syrian military", senior military officer Sergei Rudskoi said at a briefing in Moscow.
"The evacuation operation should wrap up before the OPCW experts enter Douma", Abdel Rahman said.