Two British journalists accused of "working on behalf of a terrorist organisation" in Turkey could face months in prison before learning the extent of the charges against them.

Vice News correspondent Jake Hanrahan and cameraman Philip Pendlebury were arrested while filming in the south-east region of Diyarbakir.

They were detained along with a Turkish colleague, who has not been named, while filming clashes between police and youth members of the pro-Kurdistan Workers' Party (PKK) last Thursday.

They were charged on Monday, allegedly with "assisting Islamic State" (Isis), and are due to stand trial in Turkey.

Vice News condemned the accusations as "baseless and false", with global rights and press freedom groups calling for the men's immediate release.

Amnesty International said the charges were another example of the Turkish authorities "suppressing the reporting of stories that are embarrassing to them".

Andrew Gardner, Amnesty International's Turkey researcher, said: "It is completely proper that journalists should cover this important story.

"The decision to detain the journalists was wrong, while the allegation of assisting Islamic State is unsubstantiated, outrageous and bizarre."

He added: "They are held on pre-trial detention, and they could well be there until it comes to trial.

"In Turkey it is very slow-moving and it could take six months, or even longer, for an indictment to be prepared. It could well not come to trial before six months or more."

However, this does not mean the men will be held in custody for the duration, as their lawyer will have the opportunity to challenge the detention.

Mr Gardner continued: "They were detained on the basis of what looks like a tip-off. They were questioned to do with their work, what they were doing, who they were speaking to. And they were asked if they have any connection or relations with Isis or PKK.

"All the questions related to their duties of journalism, and it doesn't look like there was any evidence of criminal activity."

PEN International and PEN Turkey - which promote literature and freedom of expression - said they "are extremely concerned" about the men's detention.

Zeynep Oral, president of PEN Turkey, said: "It is becoming increasingly difficult to carry out journalistic duties in Turkey. In a period of uncertainty, both in the country and in the region, we are in the greatest need of freedom of expression and the right to know. We ask for justice and the immediate release of journalists doing their jobs."

Commenting after the men were charged, Kevin Sutcliffe, Vice head of news programming in Europe, said the pair had been charged in an "attempt to intimidate and censor their coverage".

Vice said Mr Hanrahan and Mr Pendlebury are experienced reporters, who have together covered the migrant crisis in Calais, the Scottish referendum, republicanism, and various other stories.

Mr Pendlebury has filmed in countries like Iraq, Afghanistan and North Korea, Mr Hanrahan has also written for the Guardian, the Independent, Wired, and Rolling Stone Middle East.

A spokesman for the Foreign Office said: "We are providing consular assistance and are in touch with the relevant authorities following the arrest of two British nationals in Diyarbakir."