Many users trying to access the network early on Friday were confronted with a notice from Turkey's telecommunications authority, citing court orders for the site's apparent closure.
Twitter spokesman Nu Wexler said the company was "looking into this now," without saying whether an outage had occurred in the country.
Twitter's policy account earlier sent out messages telling Turkish users in both English and Turkish they could send out tweets by using short message service, or "SMS." It was unclear if tweets sent this way would be viewable within the country.
European Commission Vice President Neelie Kroes criticized the ban on her Twitter account as "groundless, pointless, cowardly."
"Turkish people and the (international) community will see this as censorship. It is," she said.
The Internet has in the past weeks been awash with incriminating leaked recordings, including one in which Erdogan allegedly instructs his son to dispose of large amounts of cash from a residence amid a police graft probe. Erdogan, who denies corruption, said the recording was fabricated. Links to the recordings were posted on Twitter.
At an election rally on Thursday, Erdogan vowed to take steps against Twitter regardless of "what the international community will say."
Erdogan insists the recordings are fabricated and part of plot by followers of an influential U.S.-based Muslim cleric to discredit the government ahead of the March 30 elections.
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