* Official says talks with Twitter going positively, one account shut
* US calls Twitter ban anti-democratic
* Many Turks report Internet access problems (Adds senior government official)
By Daren Butler
ISTANBUL, March 22 Turkey said on Saturday that Twitter was "biased" and had been used for "systematic character assassinations" of Prime Minister Tayyip Erdogan's government, a day after Ankara's ban on the site prompted an international outcry.
However, a senior Turkish government official later told Reuters that talks with the social media company on resolving problems which led to the block were going positively.
The Turkish authorities blocked Twitter late on Thursday, hours after Erdogan vowed to "wipe out" the social media service during the campaigning period for local elections on March 30.
Leading condemnation from Western governments and rights organisations, the White House said the Twitter ban undermined democracy and free speech in Turkey.
The site remained blocked in Turkey on Saturday. Those trying to access it found an Internet page carrying court rulings saying it had been blocked as a "protection measure".
Many Turks reported difficulties in accessing not just Twitter but the Internet as a whole, according to media reports and comments on social media.
Erdogan's office said in a statement the ban on Twitter had come in response to the company's "defiance" in failing to comply with hundreds of court rulings since last January.
"Twitter has been used as a means to carry out systematic character assassinations by circulating illegally acquired recordings, fake and fabricated records of wiretapping," the prime minister's office said.
In recent weeks, audio recordings have been released via Twitter on an almost daily basis purporting to be telephone conversations involving Erdogan, senior government members and businessmen that reveal alleged corruption.
"It is difficult to comprehend Twitter's indifference and its biased and prejudiced stance. We believe that this attitude is damaging to the brand image of the company in question and creates an unfair and inaccurate impression of our country," the statement from Erdogan's office said.
Similar measures have been taken on the same grounds in other countries to prevent violations of personal rights and threats to national security, the statement added.
Erdogan is battling a corruption scandal which he says is a plot to undermine him by a U.S.-based Turkish Islamic cleric, Fethullah Gulen. Gulen is a former ally whose network of followers include influential members of Turkey's police and judiciary. Gulen denies orchestrating the graft investigation.
Erdogan's government has responded to the scandal by tightening controls of the Internet and the courts and reassigning thousands of police and hundreds of prosecutors and judges, often demoting them.
The Turkish government began talks with Twitter on Friday, saying the ban would be lifted if the San Francisco-based firm appointed a representative in Turkey and agreed to block specific content when requested by Turkish courts.
"The talks are continuing in Ankara and the process is going positively. The biggest problem with Twitter until now has been the lack of contact and that has been resolved," the senior government official told Reuters.
He said one of the accounts to which Ankara objected had been closed and talks on others were continuing, but that it was too early to say when a solution would be reached. Turkish media reports said the closed account had contained pornographic material and did not refer to any link to the graft scandal.
"As far as we are concerned, when the court rulings are implemented the problems will be resolved and the block on Twitter will be lifted," said the senior official.
The ban stirred concerns that Turkey may pull the plug on other social media and Internet services, but the government official said there were no plans to impose restrictions on other social media like Facebook or YouTube.
Twitter said in a tweet on Friday that it stood with its users in Turkey who rely on Twitter as a "vital" communications platform. It said it hoped to have full access returned soon.
Erdogan did not talk mention the Twitter ban at election campaign rallies on Friday. He was due to address another rally in the capital Ankara on Saturday.
Many Turks have been able to get around the Twitter ban, either by using virtual private network (VPN) software or changing their Domain Name System (DNS) setting, effectively disguising their computers' geographical whereabouts.
But on Saturday morning, many people reported that computers that had been set with DNS numbers widely circulated to help people get around the ban were unable to access the Internet.
"Apparently alternate DNS servers are also blocked in Turkey. New settings are being circulated," wrote one user.
There was no official comment on whether alternate servers had been blocked. By early afternoon many on Twitter were reporting that the alternative DNS settings were working.
(Additional reporting by Orhan Coskun in Ankara; Editing by Gareth Jones)