Zambian opposition leader Hakainde Hichilema has been charged with treason after allegedly refusing to give way to President Edgar Lungu's motorcade on a main road, police said Wednesday.
Hichilema, who says he does not recognise Lungu as president, was accused of deliberately endangering his life in the high-speed incident at the weekend.
"The opposition leader disobeyed police orders to give way to the presidential motorcade in an attempt to put the life of the republican president in danger," police chief Kakoma Kanganja told reporters in Lusaka.
"The actions... were unreasonable, reckless and criminal."
Hichilema and five aides from the opposition United Party for National Development (UPND) have been charged with treason, breaking the highway code and use of insulting language.
Treason is a non-bailable offence in Zambia, with a minimum jail term of 15 years and a maximum sentence of the death penalty.
The charges were strongly condemned by the Non-Governmental Organisation Coordinating Council (NGOCC), an umbrella body of Zambian action groups
"Arresting opposition leaders on trumped-up charges is a recipe to heighten tension in an already volatile economic and political environment," its chairwoman Sara Longwe said.
The state-owned Zambia Daily Mail reported that Hichilema's motorcade ignored police attempts to clear the road between Limulunga and Mongu, 500 kilometres (300 miles) west of the capital Lusaka, on Saturday.
"The behaviour of Mr Hichilema and his cohorts was not only a senseless act of disrespect to the presidency but also endangered the life of the head of state and many other people," it said in an editorial.
More than 100 armed police surrounded Hichilema's house outside Lusaka early on Tuesday and tear gas was fired before a raid when he was taken into custody and later arrested.
The UPND has dismissed the charges and criticised the raid as "barbaric" after Hichilema's wife and children were trapped and choked by gas.
Hichilema has launched several legal attempts to challenge the August election result, which he lost narrowly.
He says that the vote was rigged and accuses Lungu of an unprecedented bout of political repression in Zambia, which has been known for its relative stability.
The election campaign was marked by clashes between supporters of Lungu's Patriotic Front (PF) party and the UPND.
International observers said the election was marred by restrictions on opposition campaigning, voter intimidation and biased state media.
Hichilema, a wealthy self-made businessman known as "HH", has run unsuccessfully for president five times.
Last October, he and party vice-president Geoffrey Mwamba were arrested for unlawful assembly and sedition when they tried to visit supporters in jail.
"HH could be detained for some time, so this will suit the ruling party who want to silence the dialogue about the election result not being recognised," independent political analyst Neo Simutanyi told AFP.
Zambia, Africa's second biggest copper producer, recorded GDP growth of three percent last year -- its slowest rate since 1998.