The US thinks it is “extremely unlikely” Turkey used chemical weapons during its offensive against the Kurds in northern Syria, a White House official said.
The US was aware of the reports but could not confirm them, the official said, according to the Associated Press.
Ankara denied accusations it has done so, saying such reports were “baseless” and Turkey has “never used” chemical weapons in Syria.
Last month, Turkey launched a military operation, dubbed “Olive Branch”, on the Kurdish-controlled enclave of Afrin supporting Syrian rebels with ground troops and air strikes against the Kurdish People’s Protections Units (YPG) militia, which Ankara views as a terrorist organisation.
Turkey says the YPG is linked to the outlawed Kurdistan Workers' Party (PKK), which has been waging an insurgency against the Turkish state since 1984.
According to Syria’s state-run Sana news agency, six people were treated in an Afrin hospital on Friday after suffering breathing difficulties and showing signs indicative of poison gas inhalation.
The Turkish military repeated in a weekly statement published on Saturday that it does not use internationally "banned ammunition" in its Afrin operation.
The UK-based Syrian Observatory for Human Rights monitor said shelling from either Turkey or allied factions hit Al Sheikh Hadid, west of the town of Afrin, and left six people with "enlarged pupils" and "breathing difficulties".
Observatory chief Rami Abdel Rahman could not confirm whether toxic gases were used, reported the Agence France-Presse.
The PKK is blacklisted as a terror group by the US and EU. But the YPG has been working closely with Washington to oust ISIL from Syria, which has strained relations between the two Nato allies.
The Observatory says at least 78 civilians have died during Turkey’s operation but Ankara repeatedly insists it is taking all the necessary measures to protect civilians.