News of a violent crackdown has emerged despite the government blocking social media sites.

Local rights groups said at least 12 people had been killed and many more beaten by security forces.

The protests were sparked on Monday by a sharp rise in the price of fuel.

President Emmerson Mnangagwa said on Sunday he was cutting short his current foreign tour to return home "in the light of the economic situation".

Presidential spokesman George Charamba, speaking to the state-owned Sunday Mail newspaper, blamed the opposition Movement for Democratic Change (MDC) for the violence that has accompanied the protests.

"The MDC leadership has been consistently pushing out the message that they will use violent street action to overturn the results of [last year's] ballot," he said.

 Hundreds of people have been arrested during the crackdown this week

The opposition rejected a court ruling in August that confirmed that President Mnangagwa had beaten MDC candidate Nelson Chamisa.

Over the course of the week riot police have clashed with protesters in the capital, Harare, and the southern city of Bulawayo after they lit fires and blocked roads using rocks.

On Thursday, Mr Chamisa tweeted that his thoughts were "with the victims of violence".

"Despite the vitriol," he added, "we maintain a dignified position befitting our role as led by the people."

The UN has called on the government to halt the "excessive use of force" by security forces, amid reports of door-to-door searches and the use of live ammunition.

Why has the fuel price increased?

A week ago, President Mnangagwa announced that the fuel price would more than double.

The price rise was aimed at tackling shortages caused by an increase in fuel use and "rampant" illegal trading, he said.

But many Zimbabweans, worn down by years of economic hardship, suddenly found they could not even afford the bus fare to work.

The new prices mean Zimbabwe now has the most expensive fuel in the world, according to GlobalPetrolPrices.com

Earlier in the week, protesters in Bulawayo blocked the main road leading to the city

They feel that the president, who has been on a tour of Russia and Asian countries, is failing to live up to his promises following his election last year in disputed polls.

The president announced his decision to return early on Twitter, saying his trip had been "highly productive" but that his "first priority is to get Zimbabwe calm, stable and working again".

Mr Mnangagwa had been expected to attend the World Economic Forum in Davos, Switzerland, this week.

But he has been struggling to revive the economy, which is experiencing high inflation while wages have stagnated.

Access to the internet was intermittent throughout the week, but people found they were unable to use social media and the WhatsApp messaging platform, which has become a common way to share news.