A German chemical wholesaler, Brenntag, has denied circumventing EU export rules on restricted chemicals, some of which were delivered to Syria in 2014.
A Swiss subsidiary of Brenntag supplied isopropanol and diethylamine to Syria. They can be used in pharmaceuticals, but can also be used to make the nerve agents Sarin and VX.
Brenntag says the deliveries also complied with Swiss law.
UN experts say Syrian government forces have used chemical weapons repeatedly.
Brenntag confirmed that isopropanol and diethylamine were delivered to Syria via its subsidiary Brenntag Schweizerhall AG, "in accordance with applicable law".
"Brenntag did not circumvent EU export restrictions," a company statement said. The chemicals were intended to produce an analgesic, it said.
Shares in Brenntag fell about 6% on Wednesday.
Brenntag, based in the German city of Essen, describes itself as the global market leader in chemical distribution. It operates in 76 countries and has more than 16,600 employees.
Its Syria deal was first reported by Germany's Süddeutsche Zeitung, broadcaster Bayerischer Rundfunk and Swiss group Tamedia.
In March the UN Commission of Inquiry probing the Syrian war said the forces of President Bashar al-Assad were behind 32 out of 37 chemical attacks during the period 2013-2019, including the use of chlorine and Sarin.
The Syrian government denies using chemical weapons.
In 2014 experts from the UN and Organisation for the Prohibition of Chemical Weapons (OPCW) removed or destroyed 1,180 tonnes of declared toxic agents and precursor chemicals in Syria, under a deal reached with the Assad government, after a Sarin attack near Damascus.
But further chemical attacks were reported later, as the fighting continued.
Between March 2013 and March 2019, the @UNCoISyria publicly reported 37 instances of the use of #chemicalweapons in #Syria. The vast majority of these attacks (32 of 37) were perpetrated by Syrian Government forces, including through the use of #chlorine and #sarin. #HRC40 @OPCW pic.twitter.com/JN9pYguPJp— UN Syria Commission (@UNCoISyria) March 12, 2019
Concerning Brenntag's chemical exports, Reuters news agency quotes Essen prosecutors as saying they have received a complaint from three non-governmental organisations: New York's Open Society Justice Initiative, Berlin's Syrian Archive and Switzerland's Trial International.
The prosecutors have not yet decided whether to open a formal investigation into the deliveries.