Rusnok's conversation with Defense Minister Vlastimil Picek in parliament yesterday was broadcast by the Czech public television news channel.
When Picek reminded him that President Milos Zeman might be unable to fly due to a knee injury, Rusnok reacted with a vulgar term.
Addressing his companion by the Czech equivalent of "dude," Rusnok said, "I'm dreading that I will have to go." He complained that he had other plans, a lunch and a dinner, and that a South Africa trip would be too long.
"I apologise for those words," Rusnok said in a statement sent to The Associated Press by his spokeswoman Jana Jaburkova today. "It was not right to use such terms in connection with the death of Nelson Mandela."
Rusnok said it would be difficult for him to find time for unexpected events in his busy December schedule. He said it will be decided in next few days who will represent the Czech Republic at Mandela's December 15 funeral.
Mandela visited Prague in 1992 to meet with then-President Vaclav Havel who had led the 1989 Velvet Revolution that ended 40 years of communism in his country. The two leaders had both spent years in prison for opposing repressive regimes before becoming presidents. They reportedly became good friends. Havel died in 2011.