A crackdown last week on protests in Zimbabwe is a foretaste of how the government will respond to future unrest, the president's spokesperson was quoted saying on Sunday, fuelling concerns that the southern African country is reverting to authoritarian rule.

Police say three people died during demonstrations that turned violent in the capital Harare and second city Bulawayo. But human rights groups say evidence suggests at least a dozen were killed, scores were treated for gunshot wounds and hundreds were detained.

"[The] government will not stand by while such narrow interests play out so violently," President Emmerson Mnangagwa's spokesperson George Charamba told the state-controlled Sunday Mail newspaper. "The response so far is just a foretaste of things to come."

Mnangagwa, who has been on a four-nation European tour and was expected to attend the World Economic Forum in Davos this week to pitch for investment to revive Zimbabwe's crippled economy, said he was instead returning home.

4 opposition members in custody

"In light of the economic situation, I will be returning home after a highly productive week of bilateral trade and investment meetings. The first priority is to get Zimbabwe calm, stable and working again," Mnangagwa posted on Twitter.

Charamba, who has been accompanying Mnangagwa on the trip, said the authorities would review some provisions of the constitution adopted in 2013, which he said were being abused by proponents of democracy.

Lawyers and activists say hundreds of Zimbabweans are in custody accused of public order offenses, including at least four lawmakers from the opposition MDC party, and Evan Mawarire, a pastor who rose to prominence as a critic of former leader Robert Mugabe and led a national shutdown in 2016.

Local rights groups say security forces, accused of night raids and beating suspected protesters in their homes, were on Sunday trying to track down people who have gone into hiding.

Partial internet blackout

A partial internet blackout was still in force on Sunday, two days after mobile networks sent messages to customers saying they had been ordered to keep social media sites shut until further notice.

Before winning a contested election in July, Mnangagwa promised a clean break with the 37-year rule of Mugabe, who used the security forces to quell civilian protests before being forced out in a de facto coup in November 2017.

Zimbabwe's President Emmerson Mnangagwa speaks during his meeting with Belarussian President Alexander Lukashenko in Minsk, Belarus, on Thursday. Mnangagwa says his first priority is to get Zimbabwe calm and "stable." (Natalia Fedosenko/Reuters)

But the MDC says former Mugabe ally Mnangagwa, nicknamed the Crocodile, is now overseeing a reversion to authoritarian rule by using the same tactics.

Charamba said the MDC leadership and affiliate organizations would be "held fully accountable for the violence and the looting." The MDC denies fomenting unrest.

UN rights officials denounced last week's crackdown, while an independent inquiry found that the army used excessive force when it stepped in to stop post-election violence last August, during which six people were shot dead.

Zimbabweans, who have seen their purchasing power eroded by soaring inflation, also say Mnangagwa has not delivered on pre-election pledges to kick-start economic growth after Mugabe's exit.