"The dire economic situation is now impacting negatively on the realization of the economic and social rights of millions of Zimbabweans".
He also said MDC leader Nelson Chamisa had rejected his invitation to dialogue meant to resolve Zimbabwe's political and economic problems.
"The Zimbabwe Republic Police (ZRP) informs the nation that based on the notifications given by MDC A to regulating authorities to hold demonstrations in Harare, Bulawayo, Gweru, Masvingo, Mutare and surrounding towns on August 16, 19, 20, 21 and 22, intelligence and concrete evidence on the ground has revealed that indeed these so called "peaceful" demonstrations will turn out to be violent", Police national Spokesperson Assistant Commissioner Paul Nyathi has said. Instead, Zimbabweans are enduring shortages of USA dollars, fuel, bread and rolling power cuts.
"Life in Zimbabwe today is worse that it was under [former president] Robert Mugabe", MDC politician Fadzayi Mahere told the BBC. "We must continue on the path or reforms in spite of temporary hardships for a better tomorrow". The cost of living has soared exponentially.
Amnesty global criticised "an escalating crackdown against human rights defenders, activists, civil society leaders and members of the opposition, including abductions and torture".
Also, he further urges the Senate when reviewing the Maintenance of Peace and Order Bill to protect the essential democratic freedoms of peaceful assembly and demonstration by ensuring Bill's compliance with the Constitution, decisions of the Constitutional Court, and worldwide human rights standards.
Ahead of Friday's demonstrations, a coalition of rights groups said six Zimbabwean political activists were abducted from their homes at night and beaten by armed men this week.
"Security remains on high alert and deployed to ensure safety of the citizenry and security of property", it said.Local rights group Heal Zimbabwe said in a series of tweets that police had rounded up scores of people in several of the city's townships and surrounding neighbourhoods.
The UK and USA have expressed concerns about the reports. Elected after the armed forces intervened to oust Robert Mugabe, Mnangagwa has said he aims to break with the long legacy of repression that characterized much of his predecessor's 37 years in power.
Mr Mnangagwa, a long-time ally of Mr Mugabe, won an election in July 2018. "Real change is the only answer to Zimbabwe's questions".
Inflation is at a 10-year high, shrinking Zimbabweans' salaries and pensions.
In recent months millions have been hit by soaring prices of food and fuel, while foreign exchange shortages have led to a lack of vital medicines and other goods.
The opposition denies this, saying the protests were peaceful.
The demonstration, dubbed "Free Zimbabwe March" is scheduled for this Friday in Harare before spilling to other major towns and cities.