A deadly car-ramming attack on a Christmas market in Germany has cast a “dark shadow” over this year’s celebrations, the nation’s president said on Tuesday, as he urged people not to be driven apart by extremists.

In his traditional Christmas address German president, Frank-Walter Steinmeier, sought to issue a message of healing four days after the brutal attack in the eastern city of Magdeburg killed five people and left more than 200 wounded.

“A dark shadow hangs over this Christmas,” said the head of state, pointing to the “pain, horror and bewilderment over what happened in Magdeburg just a few days before Christmas”.

He made a call for national unity as a debate about security and immigration is flaring again: “Hatred and violence must not have the final word. Let’s not allow ourselves to be driven apart. Let’s stand together.”

His words came a day after the far-right Alternative for Germany (AfD) held what it called a memorial rally for the victims in Magdeburg, where one speaker demanded that Germany “must close the borders”.

Nearby an anti-extremist initiative was held under the motto “Don’t Give Hate a Chance”.

Steinmeier recognised that there was a “great deal of dissatisfaction about politics” in Germany but insisted that “our democracy is and remains strong”.

A Saudi doctor, Taleb al-Abdulmohsen, 50, was arrested on Friday at the scene of the attack in which a rented SUV ploughed at high speed through the crowd. Abdulmohsen, a consultant psychiatrist, is being held in police custody on suspicion of murder, attempted murder and grievous bodily harm.

Questions are mounting in Germany about whether Friday’s attack in Magdeburg, which killed five people, might have been preventable. Reports have emerged about lapses in security, questionable immigration decisions and attempts by police to confront Abdulmohsen over threatening behaviour that were allegedly not followed through.

Days after Germany’s deadliest attack in years, a motive remains unclear.

A source close to the Saudi government told Agence France-Presse that Saudi authorities had previously requested the extradition of Abdulmohsen, who arrived in Germany in 2006 and had permanent residency. The source did not give the reason for the request, but added that Riyadh had warned he “could be dangerous”.

Holger Münch, the head of Germany’s federal criminal police office, BKA, told German television that Germany received a warning from Saudi Arabia last year but an investigation found it too vague to act upon.

Police attempted to approach Abdulmohsen for a so-called “threat analysis” discussion but apparently let the opportunity go after failing to find him at home.

Abdulmohsen has in his many online posts voiced strongly anti-Islam views, anger at German authorities and support for far-right conspiracy narratives on the “Islamisation” of Europe.

The attack has fuelled an already bitter debate on migration and security in Germany, two months before national elections and with the far-right AfD party riding high in opinion polls.

German Christmas markets have been specially secured since a jihadist attacker rammed a truck through a Berlin Christmas market in 2016, killing 13 people.

The Magdeburg event too had been shielded by barricades, but the attacker managed to exploit a five-metre gap.

In Magdeburg, where a sea of flowers and candles have been left at the site of the attack, the city of 240,000 residents is trying to come to terms with what happened.

Steinmeier offered his condolences for relatives of those injured and killed “in such a terrible way” – when the attack killed a nine-year-old boy and four women aged 45 to 75.

“You are not alone in your pain,” he said. “The people throughout our country feel for you and mourn with you.”

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