In a video message on Sunday, Mansour questioned German authorities' assertion that Interpol had asked for him to be detained.

Mansour, who has been sentenced to a lengthy jail term in Egypt after he was found guilty of involvement in torture, voiced concern that his detention arose out of complicity between Berlin and Cairo.

"Investigators informed me that the request for my arrest was German and was not in response to an Interpol request," said Mansour, in a video posted on Al-Jazeera's Arabic website since his arrest. Al-Jazeera itself has described the charges against Mansour as absurd.

The journalist, who holds both British and Egyptian citizenship, was detained at Berlin's Tegel airport on Saturday while trying to board a Qatar Airline flight on its way to Doha. He was held in custody overnight ahead of a series of legal meetings.

A Cairo court has already sentenced Mansour, in absentia, to 15 years in prison on charges of taking part in the torture of a lawyer in Cairo's Tahrir Square during the 2011 uprisings.

But Mansour - who denies the allegations - said he suspected his arrest may have part of a secret deal made between Berlin and Cairo on a recent visit of Egyptian President Mohammed Abdel Fattah el-Sissi to Germany. In a video, the 52-year-old denounced the accusations against him, but said he was confident they would not be upheld.

'Shame for Germany'

"Some lawyers also informed me that it is likely that there is a secret agreement between Germany and Egyptian authorities about my case," he said. "If this proves true, it will be a shame for Germany."

"I would like to assure you that this case is false and the Egyptian coup government is too weak to succeed in bringing the German government and the EU into this," said Mansour.

Earlier, the 52-year-old Egyptian journalist had tweeted angrily over his detention.

"The question now is how the German government and Interpol have 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 el-Sissi," he said.

Scores of protesters gathered on Sunday outside the courthouse in Berlin where Mansour was being held.

"We don't understand why Mansour was detained in Berlin," said on of the protest organizers, Ali Alawady, a member of the German-Egyptian Union for Democracy. "He is an innocent journalist who is unrightfully persecuted in Egypt."

Legal wrangling

Egyptian Foreign Minister Sameh Shoukry confirmed that Egypt was seeking Mansour's handover, claiming the arrest was in response to an international request.

"Egypt is making big efforts to get him and bring him to justice," Shoukry told a local television station.

Spokesman for the Berlin prosecutor's office Martin Steltner said there would be several legal meetings ahead of any decision to extradite Mansour. On Sunday, the office said the journalist would remain in custody for another night.

Mansour, who is known for his "Without Borders" program, recently conducted an interview with the head of the al-Nusra front, an al Qaeda offshoot fighting in the Syrian civil war.

Al-Jazeera, which is based in Qatar, has a difficult relationship with the Egyptian government, frequently accused of media suppression, since security forces arrested three of its journalists in December 2013. All were later convicted of being part of a terrorist group and airing false footage aimed at damaging Egyptian national security.

Two of the men, Mohamed Fahmy, who has Canadian citizenship, and Egyptian producer Baher Mohammed are currently free on bail amid a retrial. The third, Australian journalist Peter Greste, was deported in February.

rc/sms (AFP, AP, dpa, Reuters)