Note: This story has been updated from a previous version to include new information from WeChat owner Tencent. See full note below.

A Conservative attack ad spotted on Chinese social media giant WeChat was posted by a user without the company's knowledge, says the owner of the popular site.

The platform's owner, Tencent, says election ads aren't running on its popular WeChat social media site and it has not set up an ad registry in Canada.

"WeChat does not accept or support political ads on its platform," spokeswoman Lisa Kennedy wrote in a statement.

CBC News obtained a copy of a Conservative Party attack ad that ran on WeChat the week of October 9 in Chinese and English, claiming that a re-elected Liberal government under Justin Trudeau would legalize "hard drugs".

This Conservative Party ad appeared on WeChat. After an internal verification, the site's owner says it was posted by a user.

"Justin Trudeau's Liberals have a plan to legalize hard drugs just like they legalized marijuana," reads the ad. "Only Andrew Scheer's Conservatives will stop Trudeau's hard drug legalization plan and keep our kids safe."

The ad carries the Conservative Party's logo and says it was "authorized by the official agent for the Conservative Party of Canada." It's similar to an attack ad that appeared on the Conservative Party's official website on Oct. 9.

Members of Elections Canada's social media monitoring team also have spotted Canadian election ads on WeChat, said spokeswoman Natasha Gauthier.

"WeChat is one of the websites that they keep an eye on," she said. "The team has seen political ads on WeChat but the team is not focused on detecting potential compliance or non-compliance."

Gauthier could not say which parties or candidates' ads Elections Canada officials have spotted on WeChat.

Kennedy said Tencent conducted an internal review after the CBC reported on the presence of the Conservative ad on WeChat and confirmed it did not receive payment for it to be on the site. The company said it appears to have been posted there by a WeChat user.

"WeChat allows users to send messages or share images and videos with other users but has no role in the creation or posting of user-content on its platform," the company said in a statement. "Some user-posted content on WeChat may contain personal political views or advocacy."

She said the company has been contacted by Canadian authorities about the ad and is answering their questions.

No comment from Conservatives

Conservative campaign manager Hamish Marshall refused to comment on which social media platforms the party is using for advertising in the election.

"We don't comment on our advertising strategy," he said.

Since then, he has not responded to requests to confirm that the party placed the ad found on WeChat. The party has been running a similar ad on Facebook.

Canada's Chinese community is one of the groups the Conservative Party hopes to win over in this election.

Trudeau has denied the Liberals have any plans to legalize hard drugs.

The Liberals said they are advertising on Facebook, Instagram and Twitter, but not on WeChat.

The New Democrats said the party has focused its online advertising on Facebook and Instagram and the national campaign is not advertising on WeChat.

The new elections law

Under recent changes to Canada's elections law, online companies that accept political ads during the election campaign have to set up digital registries of all of the political ads running on their platforms, with copies of the ads and information about who authorized them. The requirement has prompted some internet giants, including Google, to stop accepting political ads in Canada during the federal election.

The law can apply to companies located anywhere in the world if the number of visitors from Canada to their sites exceeds a certain threshold.

Platforms that publish in a language other than English or French must have more than 100,000 unique visitors from Canada each month to be subject to the law. Bryan Segal, senior vice-president of Comscore (which measures web traffic), said WeChat gets an average of 616,000 unique visitors in Canada per month.

Elections commissioner can investigate

Gauthier said Elections Canada's monitors are looking for examples of online misinformation or disinformation about how and where to vote. They are not, however, responsible for checking whether an online platform that is subject to the law has set up an online registry.

Commissioner of Canada Elections Yves Côté can investigate if someone files a complaint, said Gauthier.

"It is an offence to be an online platform that meets these thresholds and to not have this registry. So that is an offence under the act," she said.

"Penalties can range from administrative monetary penalties to what the commissioner calls compliance agreements, which it publishes on its website."

However, parties and candidates are not required by law to verify whether an online platform has set up a digital ad registry before they advertise, she said.

Michelle Laliberté, a spokeswoman for Côté, said the commissioner's office doesn't "proactively carry out monitoring or surveillance of digital platforms," but it can investigate complaints.

"While I can't speak to whether or not we have received complaints in relation to this issue, if someone were to bring forward a complaint we would evaluate it to see if it falls within the Commissioner's mandate."

Elizabeth Thompson can be reached at elizabeth.thompson@cbc.ca