Turkey on Friday marked a week since the authorities blocked access to Instagram, with Human Rights Watch (HRW) saying the suspension violated free speech.
The authorities have also frozen the popular online video game Roblox.
The rights watchdog urged the government to restore access to US-owned Instagram, which President Recep Tayyip Erdogan has accused of "fascism" and ministers have blamed for failing to remove posts the authorities deem offensive.
"Blocking everyone's access to an entire social media platform is a grossly disproportionate measure that violates the right to free expression and information of millions of users," HRW's Deborah Brown said.
"(It) should be reversed immediately."
Last week, Erdogan's communications director Fahrettin Altun accused Instagram of censorship.
He complained the platform had prevented people from posting messages of condolence over the assassination of Ismael Haniyeh.
Haniyeh, the political leader of the Palestinian group Hamas, was killed in Tehran in an attack blamed on Israel.
Erdogan, an ally of Haniyeh's, said on Monday that social media networks "cannot even tolerate photos of Palestinian martyrs without immediately banning them".
Unresolved differences
Instagram has an estimated 50-60 million subscribers in Turkey and is used by numerous businesses to trade and find customers.
The Turkish e-commerce operators’ association has calculated the ban is costing around 1.9 billion Turkish lira, or nearly $57 million, per day in lost business.
Yaman Akdeniz, a co-founder of the Freedom of Expression Association (IFOD), said the freeze on Instagram was "disproportionate and arbitrary", stressing that it had been introduced "without a (prior) court order".
Transport and Infrastructure Minister Abdulkadir Uralolu met Instagram representatives on Monday but their differences have yet to be resolved.
Uraloglu said last week the platform, which is owned by US tech giant Meta, had been suspended for ignoring demands to remove "criminal content".
An anonymous source at Turkey's BTK communications authority said these included "insults to Ataturk", the founding father of modern Turkey, "drugs (and) pedophilia".
Meta said it had taken down more than 2,500 posts flagged by the government in the first six months of the year.
On Wednesday, the authorities also banned Roblox, a platform that allows players to create their own games and has been downloaded more than 41 million times in Turkey.
Justice Minister Yilmaz Tunc alleged "it contains content that will cause abuse of children".
Prosecutors in Adana are investigating it.