Zambian authorities on Wednesday arrested singer and activist Chama Fumba at Lusaka airport in a move condemned by Amnesty as a "shocking demonstration" of the government's intolerance of criticism.Fumba, popularly known as Pilato, was picked up by plain-clothed police officers as he arrived home from South Africa after four months abroad, eyewitnesses said.Pilato fled Zambia after receiving threats from supporters of the ruling Patriotic Front party over his hit song "Koswe Mumpoto" ("Rat in the pot").The song was widely seen as accusing President Edgar Lungu and his ministers of being corrupt."We should be careful with these rats... They want kickbacks in everything in the search for cheese," says one lyric in the song.Last month, an arrest warrant was issued for Pilato after he failed to appear in court while abroad.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and FacebookPilato was due in court for protesting last year against the procurement of 42 fire-fighting vehicles at a cost of $1million each - an example of alleged graft under Lungu.Amnesty International said the arrest warrant was incorrectly issued and the criminal justice system was being misused for political reasons.His arrest "shows the lengths to which Zambian authorities are prepared to go to stifle dissent," said Amnesty's southern African director Deprose Muchena."Pilato just landed. Whisked away by plain clothes police," fellow activist Laura Miti posted on social media on Wednesday.Police spokeswoman Esther Katongo declined to comment, saying the case was already before the courts.In 2015, Pilato was arrested for conduct likely to cause the breach of peace after he released another song depicting a character called Lungu carrying a suitcase filled with whisky. He was later released after the state dropped the charges.President Lungu has been accused of a crackdown on dissent since winning elections in 2016.