The three, reporting for US-based media outlet Vice News, were detained on Monday and remanded in custody in the mainly Kurdish southeastern city of Diyarbakir in a case that has caused international concern.

They have been charged with "engaging in terror activity" on behalf of the Islamic State extremist group.

Vice News has condemned the charges as "baseless" and "alarmingly false".

The three have now been transferred to a jail in Adana, the head of the Diyarbakir bar association Tahir Elci and legal sources told AFP.

Elci said the reason given for the move was a lack of available English-speaking translators in Diyarbakir.

"This is another example of the mistreatment against the detainees," Elci said.

Legal sources said that even though they were being held in Adana, the investigation would continue to be based in Diyarbakir -- 500 kilometres (300 miles) northeast.

- 'Badly needed coverage' -

Vice News slammed the prison transfer, describing it as a "blatant obstruction of the fair legal process that Turkey has repeatedly pledged to uphold."

It said that the journalists "have now been transported to a prison facility more than five hours away from where their legal representation is based, and from the court where they are due to appear.

"We call on the Turkish government to throw out these ridiculous charges and immediately release our colleagues."

Their detention has drawn criticism from across the world and amplified concerns about declining press freedoms in Turkey.

In its first reaction to the controversy, the Foreign Office in Britain said it was "concerned" about the arrest of the two British nationals.

"Respect for freedom of expression and the right of media to operate without restriction are fundamental in any democratic society," it said in a statement, saying it expected the Turkish authorities to uphold their human rights obligations.

It said the journalists have been given access to a lawyer and were in direct contact with consular officials within 24 hours of their detention.

Vice News, which produces in-depth Internet video reports for the Internet, has named the British journalists as Jake Hanrahan and Philip Pendlebury.

The team had been visiting the region as the government wages a relentless campaign against Kurdistan Workers' Party (PKK) militants, with several local Kurdish officials arrested and accused of supporting declarations of self rule.

A Turkish official on Tuesday denied Ankara played a role in the arrest of the Vice team and said the government is "not pleased" they are being held.

In a letter to Turkish Prime Minister Ahmet Davutoglu, the executive director of the Committee to Protect Journalists Joel Simon called on him "to do all that you can to ensure that these journalists are released."

He said the reporters were "providing badly needed coverage of current events in southeastern Turkey".