German authorities have released al-Jazeera journalist Ahmed Mansour

German authorities have released al-Jazeera journalist Ahmed Mansour without charge, after he was detained on Saturday by police at Berlin’s Tegel airport on an Egyptian arrest warrant.

A spokesman for the state prosecutor said there were “political and diplomatic concerns that could not be ignored” in addition to the legal aspects of the case. These concerns, he said, were discussed with the Berlin state justice minister and the appropriate federal authorities.

A lawyer for Mansour, who has dual Egyptian and British citizenship, told al-Jazeera that while his client was happy about the court’s decision, he was also sad that he had been detained.

Questions remain as to why the German authorities arrested Mansour at the behest of Egypt’s military regime in the first place, and why they waited until he was at the point of leaving Germany to do so.

There was considerable confusion over the warrant, which a German government spokesman said on Monday came via Interpol’s “red notice” system, though both Mansour and Interpol said no such red notice exists against his name.

According to police spokesman Meik Gauer, the arresting officers at Tegel airport were answerable only to the federal police headquarters, not to Interpol. There also remains a question mark over why the police officers felt obliged to detain Mansour, given that Germany does not have an extradition agreement with Egypt.

Cologne-based lawyer Nikolaos Gazeas told Zeit Online: “Germany is not under a legal obligation to extradite to Egypt. That is ultimately a political decision.”

For that reason, legal commentators have suggested the warrant could not have been executed without consultation with the government.

Last year, an Egyptian court convicted Mansour in absentia of torturing a lawyer in Tahrir Square in 2011 and sentenced him to 15 years in prison. Mansour rejected the charges, calling them “a flimsy attempt at character assassination”.

On Monday morning, a group calling itself the German-Egyptian Union for Democracy gathered about 100 protesters outside the Berlin jail where Mansour was being detained. They held signs that read: “Freedom for Ahmed Mansour. Freedom for Egypt. Freedom for journalists.”

MPs across Germany’s main political parties had voiced concern over his detention. Among the most outspoken was the opposition Green party’s Franziska Brantner, who said in a statement on her website: “The Berlin judiciary should under no circumstances allow itself to become a willing tool of the capricious regime in Cairo.”

Egypt accuses both Qatar and al-Jazeera of supporting the Muslim Brotherhood, which was branded a terrorist organisation after the military deposed Mohamed Morsi as president in 2013. Three journalists with al-Jazeera English spent more than 400 days in prison following their arrest in Cairo in late 2013. Their trial was regarded internationally as a farce.

Angela Merkel, the German chancellor, was criticised by opposition parties and rights groups for hosting the Egyptian president, Abdel Fatah al-Sisi, on a state visit this month. During the visit, the German industrial group Siemens signed an €8bn deal with Egypt to supply gas and wind power plants.

Since Sisi took power in 2013 and won a presidential election the following year, courts in Egypt have issued scores of death sentences against Muslim Brotherhood members including the group’s leadership.