Daniel Hauer lives in Vietnam, is married to a local woman and speaks fluent Vietnamese.

He has a wide local following on Facebook and Youtube for his English language teaching videos and his observations about Vietnamese and Western culture.

But a joke about General Vo Nguyen Giap triggered widespread condemnation on social media. Hundreds of people are calling for him to stop teaching and leave the country.

He has since posted an apology video, was summoned by the authorities and is now facing a fine or a warning. It is thought to be the first time a foreign citizen has had to appear before officials for comments posted online.

Communist Vietnam has a high rate of social media usage, but exercises strict control over the internet, filtering out content deemed undermining of the government of its values.

Tight control

Its censorship rules have often been used to silence government critics and several dissident bloggers have been jailed.

On Wednesday, three activists Vu Quang Thuan, Nguyen Van Dien, and Tran Hoang Phuc were sentenced to between six and eight years in jail for distributing propaganda against the state.

In 2017, popular environmental blogger Mother Mushroom received a 10-year prison sentence under similar charges.

The same year, 22-year old blogger Nguyen Van Hoa was sentenced to seven years for writing about a toxic spill from a factory poisoning millions of fish.

In 2015, activist lawyer Nguyen Van Dai was arrested without trial after already having served a lengthy sentence previously.

Mr Hauer's controversial comment was trivial, in comparison.

It came last week, when the country was swept up in a wave of patriotism after its under-23s football team made it all the way to the finals of the Asian Cup, Vietnam's biggest ever football success.

A Facebook commentator had said he would get a tattoo of the Vietnamese flag, should the country win.

In a hyperbolic joke, the English teacher said that was nothing - after a Vietnamese athlete recently won a gold medal, he said, he'd got a penis piercing making his testicles resemble Gen Giap.

General Vo Nguyen Giap is revered for leading successful military campaigns against both the French and the US. He passed away in 2013, receiving a grand funeral.

Fury and condemnation

Mr Hauer's flippant remark first caused widespread protests online and eventually made it into the news on national state television.

Many online commentators were not holding back with furious condemnation, asking for him to be deported, leave the country and accusing him of gross cultural insensitivity.

Yet there are also other comments pointing out that a sincere apology would be enough to eventually set things straight again while some even sympathise with him.

The grandson of Gen Giap also publicly shared his anger about the post, initially in a strongly worded comment and which he later replaced with a more toned down one saying "millions of people who love him Gen Giap felt the anger caused by this foreigner's insult".

'Not meant as an insult'

But Mr Hauer was also in trouble with the authorities.

A controversial law introduced in 2013, known as Decree 72, bans online activity if it falls under certain categories, including opposing the government, harming national security or insulting honour and dignity of organisations and individuals.

Mr Hauer's comments are thought to fall under the latter category,

The US citizen, who declined to speak to the BBC, has apologised for his post, saying he had made a distasteful joke but had not meant it as an insult to the general or the Vietnamese people.

He added that the reaction to the post had taught him a lesson and that he wanted to personally apologise to the family of the general.

According to officials, he now faces a warning or a fine of up to 100m Vietnamese Dong ($4,390; £3,131).

Fellow expat Cameron Lucy runs a Facebook group for foreigners in Hanoi and appeared on Vietnamese TV to comment on the case.

He told the BBC that Mr Hauer likely "didn't understand how serious the situation was."

"It is never a good idea to insult a national hero, especially when you're a visitor to that country. I'm sure Dan is really regretting his comment now and very sorry for that."

By Hoang Nguyen & Andreas Illmer - BBC Vietnamese - February 1st, 2018