A renowned Al-Jazeera journalist was being held in German police custody Sunday pending a court decision on his further detention on an arrest warrant issued by his native Egypt.

In a case that raised issues about press freedom and German relations with Egypt under President Abdel Fattah al-Sisi, reporter Ahmed Mansour was arrested Saturday at a Berlin airport having been accused by Cairo of committing "several crimes".

"He is in police custody," a spokesman for the Berlin public prosecutor's office, Martin Steltner, told AFP Sunday.

"The Berlin prosecutor's office is examining the legal assistance request" from Egypt, he added.

Mansour, who also has British citizenship, is to appear before a judge, who is to decide as early as Sunday whether to keep him in detention and launch extradition procedures or release him, Berlin authorities said.

Al-Jazeera said on its website that an Egyptian court had sentenced Mansour in absentia in 2014 to 15 years in prison, for "torturing a lawyer in 2011 on Tahrir Square" in Cairo, epicentre of an anti-regime uprising that brought down former president Hosni Mubarak.

"Mansour has rejected these absurd accusations," the network said.

The 52-year-old journalist also told Al-Jazeera he was facing rape, kidnapping and robbery charges -- charges which he denied.

Ties between Doha and Cairo have been extremely strained over Qatar's backing for the former, short-lived Egyptian government under the Muslim Brotherhood.

Three Al-Jazeera journalists, including Australia's Peter Greste and Canada's Mohamed Fahmy, were arrested in Cairo in 2013 and sentenced to up to 10 years in prison on charges of supporting the Muslim Brotherhood.

Greste has since been deported while the other two are facing a retrial.

In a video aired by the Doha-based pan-Arab satellite channel Sunday Mansour said the charges against him were "false".

"The coup regime in Egypt is too weak to drag a state like Germany and the EU into its dirty game against Egyptians," said Mansour, referring to the Egyptian military's ouster of Islamist president Mohamed Morsi in July 2013.

In a separate video also released by Al-Jazeera, Mansour accused the German authorities of dealing with his case "in a way that raises suspicions over its role, through complicity with the regime in Egypt".

Mansour also said he had been told by police that his arrest was "based on a German order, and not due to an Interpol order".

He tweeted angrily in detention on Saturday that Berlin was colluding with Cairo.

"The question now is how have the German government and Interpol become tools in the hands of a bloodthirsty regime in Egypt that came to power through a coup, and is led by the terrorist Abdel Fattah al-Sisi."

About 50 protesters gathered outside the jail in central Berlin where Mansour was being held demanding his release.

The group calling itself the "German-Egyptian Union for Democracy" held up placards reading "Freedom for Journalist Ahmed Mansour".

German opposition politicians also sharply criticised the arrest.

"Berlin justice authorities must under no circumstances allow themselves to become the agents of Cairo's capricious regime," a deputy from the Greens party, Franziska Brantner, said in a statement.

"Germany must not extradite him."

The deputy parliamentary group head of the far-left Linke party, Wolfgang Gehrcke, told Cologne's daily Stadt-Anzeiger that the rule of law in Egypt was "fragile -- if you can even speak of the rule of law".

Mansour, who hosts a popular news programme, recently interviewed Abu Mohamed al-Jolani, the chief of Al-Qaeda's Syria affiliate, Al-Nusra Front.

While in Berlin, he interviewed an expert on Islamist militants from a prominent German think-tank.

His arrest comes hot on the heels of a visit by Egypt's Sisi to Germany on June 3.

Rights groups had urged Chancellor Angela Merkel to press Sisi to end grave rights abuses.

In a joint press conference with Sisi the chancellor voiced criticism of Egypt's use of the death penalty and record on religious freedom, but pledged closer economic ties with its partner in the fight against Islamic extremism.