Zambian police have arrested and charged an opposition leader with defamation, after he compared the president to a potato.

Frank Bwalya, head of the Alliance for a Better Zambia, allegedly referred to president Michael Sata as "Chumbu Mushololwa" during a live radio broadcast on Monday.

The Bemba term refers to a sweet potato that breaks when it is bent and is used to describe someone who does not heed advice.

"The police decided to arrest and charge him with defamation of the president," Eric Chanda, the secretary general of Alliance told AFP news agency.

If convicted, Bwalya faces a maximum jail term of five years.

Bwalya, a former Catholic priest and supporter of Sata when in opposition, is just the latest opposition leader to run afoul of Zambia's leader.

In September, Nevers Sekwila Mumba of the Movement for Multiparty Democracy was questioned by police after calling Sata a liar.

"President Sata is the same old man who was on all radio stations defaming former presidents Banda and Mwanawasa and nobody arrested him," said Chanda.

Bwalya has pleaded not guilty to the defamtion charges and has been released on bail. He is to return to court on January 21.

Bwalya denied insulting the president and said his comments were taken out of context and exergarated.

"On that radio program, I strongly criticized the bad leadership of the president. I called him a crooked sweet potato that cannot be straightened. It is a commonly used phrase which is not insulting. It is to explain the attitude of a person who doesn’t want to be advised who doesn’t want to be counseled,” Bwalya told VOA.