Turkey on Saturday blocked all access inside the country to the online encyclopedia Wikipedia, the communications agency said, in the latest restriction on a popular website to hit Turkish users.
Turkey's Information and Communication Technologies Authority (BTK) said it had implemented the ban on wikipedia.org but the reason for the move was not immediately clear.
A block affecting all language editions of the website in Turkey was detected from 0500 GMT after an administrative order by the Turkish authorities, the Turkey Blocks monitoring group, which watches internet restrictions in the country, said in a statement.
Residents in Istanbul were Saturday morning unable to access any pages of Wikipedia without using a Virtual Private Network (VPN), AFP correspondents said.
"The loss of availability is consistent with internet filters used to censor content in the country," Turkey Blocks said.
The BTK confirmed the ban in a statement but gave no details.
"After technical analysis and legal consideration based on the Law Nr. 5651, an administrative measure has been taken for this website wikipedia.org," it said.
No reason was given for the order to block Wikipedia. Other websites, including leading social media, appeared to be working normally.
Turkey Blocks said the restriction was in place with multiple Internet Service Providers (ISPs).
Turkey has become notorious over the last years for temporarily blocking access to popular sites, including Facebook and Twitter, in the wake of major events such as mass protests or terror attacks.
Savvy internet users frequently resort to the use of VPNs to get around these bans although there have been complaints that the use of VPNs has now also started to be blocked.
The government says such measures are always temporary and needed for national security but critics see them as another restriction on civil liberties under President Recep Tayyip Erdogan.
In November 2016, Turkey imposed major temporary restrictions lasting for several hours on messaging service WhatsApp as well as Twitter, Facebook, YouTube and other sites following the controversial arrests of pro-Kurdish MPs.
Prime Minister Binali Yildirim then acknowledged that "from time to time for security reasons we can use such measures... These are temporary measures. Once the danger is passed, everything returns to normal."
The move to block Wikipedia caused an uproar on social media in Turkey with users angrily denouncing the decision to restrict access to one of the world's most popular websites.
Some speculated the decision may have been prompted by deeply unflattering updates by critical users to Erdogan's Wikipedia profile after he won the April 16 referendum on enhancing his powers.
Pro-government bloggers said at one point after April 16 Erdogan had been described as a "dictator" on his main Wikipedia profile.
The government insists that the new presidential system -- largely due to come into force in 2019 -- will improve efficiency, but critics fear it will lead to one-man rule.