Saudi authorities have called on the public to supervise and report on the social media activities of fellow citizens, while issuing broad definitions of "terrorist" crimes.
"When you notice any account on social media spreading terrorist or extremist ideas, please report it immediately," a Twitter account under the umbrella of the interior ministry said late Tuesday.
It directed citizens to report suspicious activity via a government-run "We are all security" mobile application.
The app was created in February 2017 but only this week took on a political dimension, having previously been geared toward reporting traffic violations and theft.
The Twitter call for citizen vigilantism was followed by two tweets from the public prosecutor's office issuing broad definitions of what constitute "terrorist crimes" in the kingdom.
"Endangering national unity, obstructing the constitution or its articles, or harming the reputation of the state is a terrorist crime," the first tweet read.
It later added to the list of offences: "Any action committed by an individual criminal or group -- directly or indirectly -- intended to disrupt the public order or destabilise the security of the state or society."
A group calling itself the "15 September Movement" has called for nationwide demonstrations in Saudi Arabia on Friday to protest poverty and advocate for women's rights and the release of detainees.
The group's Twitter account, which has more than 9,000 followers, condemns "those who surrendered the sovereignty of the country at the feet of (US President Donald) Trump".
Saudi Arabia, with its bulging youth population, is among the top users of social media per capita worldwide. The internet represents a limited space for freedom of expression in the conservative kingdom.