German President Frank-Walter Steinmeier described the knife attack in which a police officer was fatally injured on market square as a "bloody act of terrorism."
Steinmeier spoke said during a ceremony commemorating the death of police officer Rouven Laur in Mannheim on Friday, attended by many of his colleagues and citizens of the western city.
Laur, 29, died in an attack on Sunday, days after he was injured as he sought to intervene when a man attacked several people during a rally by the anti-Islam movement Pax Europa in Mannheim.
Steinmeier, state premier Winfried Kretschmann and state interior minister Thomas Strobl all paused for a minute's silence at 11:34 am.
In recent weeks, there have been further "heinous acts of politically motivated violence" with attacks on mayors, ministers, members of parliament and volunteers, Steinmeier said.
"We, the democrats of this country, must never and will never get used to violence in political disputes."
Steinmeier laid a floral tribute at the scene as many gathered on the square to mourn the death of the policeman.
Some 50 officers from the city's police headquarters, mainly patrol officers, a spokeswoman said, lined up in front of a sea of flowers laid on the market square and clasped hands as they paid tribute to their colleague. Onlookers applauded.
The 25-year-old Afghan also injured five participants at the rally on May 31.
A slew of demonstrations are planned for later. The far-right Alternative for Germany (AfD) party plans to demonstrate on the square against Islamism at 6 pm. A counter-demonstration by thw anti-fascist organization Antifa is to take place at the same time.
At 4:30 pm, a rally is planned under the motto "Mannheim stands together - for democracy and diversity," organized by the local branch of the German Trade Union Federation and representatives of democratic parties and religious communities.
A demonstration against the AfD rally is planned at 5:30 pm by the "Mannheim against the Right" alliance.
On Thursday, the Karlsruhe Administrative Court granted an urgent appeal by the AfD against a general order by the city which banned events such as demonstrations on the market square.
On Tuesday, the city had temporarily declared the market square a memorial site for the dead police officer and banned events such as demonstrations.
