Western states have blamed the Syrian government forces for the incident, but Damascus has denied using chemical weapons.
Medical student Marwan Jaber said no chemical weapons were used on April 7.
On Monday, the AP visited a two-room underground shelter where Khaled Mahmoud Nuseir said 47 people were killed, including his pregnant wife and two daughters, 18-month-old Qamar and 2 1/2-year-old Nour.
The US, UK and France say that, based on open source information and their own intelligence, they are confident chlorine and possibly a nerve agent were used.
Meanwhile, the U.S. and France say they have evidence that poison gas was used in Douma, east of Damascus, killing dozens of people, and that President Bashar Assad's military was behind it, but they have made none of that evidence public. It also reported a separate air strike on the Dumayr air base near Damascus.
Inspectors not allowed into Douma: UK envoy
Residents say they worry that Syrian authorities and their Russian allies are whitewashing the history of April 7. The Kurdish-led SDF have been of the U.S.'s most trusted allies in Syria in its war on the Islamic State group.
Syrian and Russian forces gained control over Douma on Saturday when rebels withdrew from the town, hours after the end of the Western countries' attacks.
The official says Haley was unaware that the administration's plans to impose fresh sanctions on Russian Federation over its support of the Syrian government had been put on hold.
"It was in our national interest and it is a decision that should be, I believe, supported by everybody who recognises that we need to re-establish the worldwide norms in relation to the use and the prohibition of the use of chemical weapons".
"These strikes don't necessarily resolve anything but I think they were important", he said.
Al Jazeera's Khodr said that even if the OPCW finds that the chemical weapons attack happened, there would be no new punitive strikes.
On April 16, the head of the global chemical-weapons watchdog said that inspectors had not yet been granted access to the site.
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Syria and Russian Federation deny unleashing poison gas on April 7 during their offensive on Douma, which ended with the recapture of the town that had been the last rebel stronghold near the capital, Damascus. Israel did not confirm or deny mounting the raid.
But "strangers entered as we were in a state of chaos and spread a rumour among people there had been a chemical attack, and people became alarmed".
As CBS News correspondent Seth Doane reports, rebel forces had held Douma nearly since the start of the war in Syria, now more than seven years old, and the government's fight to take it back was fierce.
Russian Foreign Minister Sergey Lavrov told the BBC's "HARDtalk" that he guaranteed there had been no Russian tampering, adding his country had sent experts to the site and found "no trace" of chemical weapons. Britain denies the allegation.
"While searching the site, the Russian nuclear, chemical and biological-warfare units have found substances that fall under the Convention for the Prohibition of Chemical Weapons", Colonel Aleksandr Rodionov, an officer with the Russian nuclear, chemical and biological-warfare troops, told journalists.
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