The rare kidnapping in the occupied West Bank took Muslim anger to a new level in a controversy over balancing Western freedom of the press with religious sensibilities.
In the Gaza Strip, where tensions are also high, a hand grenade was thrown into the compound of the French Cultural Centre. No one was hurt in the night-time incident, security officials said.
Palestinian security officials said gunmen from a militant faction in President Mahmoud Abbas's Fatah faction seized Christoph Kasten, 21, from a hotel coffee shop in the city of Nablus and took him to an empty field before releasing him.
There was no immediate word from the kidnappers on their motives, but the security officials said the militants were showing their anger at publication of the cartoons in Denmark, Norway, France, Germany and Spain.
Islamic tradition prohibits realistic depictions of prophets, and considers caricatures of them blasphemous.
"Two Palestinian gunmen asked me to go with them. I didn't know where.They did not make any demands"
German kidnap victim
"Yes, I am OK," Kasten, an English teacher, told reporters in the offices of the Preventive Security agency in Nablus. "Two Palestinian gunmen asked me to go with them. I didn't know where. They did not make any demands. After a while, they put me in a taxi and told me the taxi would take me to the police."
Earlier, al-Aqsa Martyrs Brigades, an armed faction in the Fatah movement, threatened in a news conference to kidnap citizens of France, Denmark and Norway if they did not leave Nablus within 72 hours.