Soldiers patrolled city streets on Tuesday as banks, schools and businesses stayed shut and confrontations with demonstrators threatened to boil over, a day after protests over Zimbabwe's worst economic crisis in decade turned deadly.

Monday's unrest, during which several people were killed and some 200 arrested, followed sharp fuel price hikes decreed by President Emmerson Mnangagwa, who impatient Zimbabweans accuse of failing to live up to promises to kick-start growth.

Mnangagwa, absent on an official visit to Moscow, has also promised a clean break from the oppressive regime of long-term leader Robert Mugabe, who he forced out in a de facto coup in November 2017.

But as witnesses reported security forces deploying in Harare and Zimbabwe's second city Bulawayo, many people in the capital said they could no longer access the internet.

A human rights lawyers group said it had received reports of soldiers and police officers breaking into homes in Harare townships overnight and assaulting suspected demonstrators.

Defence Forces spokesman Overson Mugwisi, police spokeswoman Charity Charamba said they could not immediately comment, as did the country's three mobile telecoms firms.

In Moscow, Mnangagwa said Zimbabwe might need Russia's help in modernising its army and was interested in receiving Russian loans, RIA news agency quoted him as saying.