The cartoon is one of 12 images first published in a Danish newspaper in 2005, sparking Muslim protests in many countries.
The posters, which say "Freedom is not for free," appeared this week in Brno, the second-largest Czech city. It was unclear who put them up, but they were signed by "Friends of Freedom of Speech."
The Czech Foreign Ministry condemned all actions insulting religious beliefs or inciting hatred.
"Prophet Mohammed did not know any bombs at his time. It is a sheer mockery," Schwarzenberg said in a statement issued late Wednesday.
"I find it sad ... It has nothing to do with the freedom of speech," he said.
Brno's Muslim community was unfazed. People who believe that Muslims "do not honour freedom" are wrong, the Denik newspaper cited local Islamic Foundation head Muneeb Hassan Alrawi as saying.
About 8,000 Muslims live in Czech Republic, a Central European country of 10 million people.
Güncelleme Tarihi: 20 Mart 2008, 17:44