Thai authorities have arrested and charged a man for posting 'inappropriate content' online amid furore over a royal motorcade which left Bangkok traffic at a standstill.

Karn Pongpraphapan, 25, was arrested under cybercrime laws as police said he 'stirred hatred' over 'inappropriate hashtags' which appeared on social media.

'Royalmotorcade' became one of the top trending hashtags on Thai-language Twitter last week after motorists in the capital were left at a standstill for an hour while the procession passed through.

Some claimed that an ambulance was left stranded in the jam, with officers telling the driver to turn their siren off as the delay dragged on.

Karn Pongpraphapan, 25, was arrested under cybercrime laws in Thailand and accused of 'stirring hatred' over hashtags which went viral last week after traffic in Bangkok was held up for an hour as a royal motorcade passed through (pictured)

While Karn's lawyer denied his arrest involved the hashtag, Thailand's deputy police chief Siriwat Deepor said he was detained after 'bad actors started inappropriate hashtags on social media.'

News of the royal motorcade holding up traffic in Bangkok became one of the top-trending subjects on Thai-language Twitter on Tuesday last week.

Frustrated motorists told of how they had been held up for more than an hour by the motorcade, while an image of an ambulance caught up in the traffic went viral.

Some alleged that police officers had approached the emergency vehicle and asked the driver to turn the siren off while it sat motionless in the jam.

Announcing the arrest, Siriwat said: 'Over the last week, bad actors have started inappropriate hashtags on social media, resulting in the arrested person posting inappropriate content on Facebook which stirred hatred.'

Police did not identify Karn but said the person they had arrested had violated a section in the Computer Crime Act which punishes anyone 'uploading computer data that affects national security' for up to five years in prison.

Siriwat said the suspect was arrested at his home on Monday.

Thailand has strict laws against insulting the monarchy, headed by newly-coronated King Vajiralongkorn (pictured), though Karn was not arrested under these laws and it is not clear which royal was involved in the motorcade

Thai law punishes insulting the monarchy with up to 15 years in prison, but no new lese majeste cases have been pursued since 2018.

Karn's lawyer said his client posted historical comments about other countries' royalty but said the post did not repeat the hashtag.

'The comments he posted on his Facebook did not mention Thailand's monarchy nor the #royalmotorcade hashtag at all,' lawyer Winyat Chatmontree said.

'His post was about the history of Russia, France, and Germany. But the charge brought on by the digital economy ministry resulted from an interpretation and an effort to link him to the hashtag,' Winyat said.

Karn had joined an activist campaign calling for elections during a period of military rule that ended with a general election this year, Winyat said.

The arrest comes less than three months after Thailand's new minister of digital economy, Puttipong Punnakanta, vowed to 'purge' social media of royal insults shortly after taking office.

Puttipong also declined to directly link the arrest to the #royalmotorcade hashtag when asked by Reuters on Tuesday, but he said that the suspect's actions were unacceptable.

'We are taking this seriously and this arrest should serve as an example to others, that they should think carefully because it can have criminal consequences,' Puttipong told reporters.

Prime Minister Prayuth Chan-ocha, who led a 2014 military coup, was elected to office in June after his party won elections in a campaign emphasising traditional values including devotion to the monarchy and implying that opposition parties were disloyal.