Ten people have been killed in the Venezuelan capital, Caracas, during a looting incident at a bakery.
Footage recorded by residents showed heavy shooting and police in armoured vehicles trying to regain control of the situation in El Valle district.
In a separate incident, a man was shot outside the capital at the end of an opposition march.
The violence comes at the end of two days of protests against the President Maduro's socialist government.
Three other people were killed during protests on Wednesday and Thursday.
The authorities blamed opposition activists for most of the deaths in the El Valle looting incident, which happened late on Thursday night.
Two people were shot dead trying to loot a bakery, while eight others stepped on a high voltage cable, which the government says was sabotaged by opposition groups.
The opposition has called for silent marches across Venezuela on Saturday to honour the people killed in protests over the past three weeks.
Early elections demanded
The latest wave of protests was triggered by a Supreme Court decision on 29 March to take over powers from the opposition-controlled National Assembly.
When it reversed its decision three days later, it was already too late to contain the opposition and street demonstrations.
Opposition leaders are calling for new presidential elections and the release of politicians arrested since Mr Maduro took office four years ago.
Venezuela is facing a serious economic crisis, despite having the world's largest proven oil reserves.
Inflation is expected to reach 700% this year, according to the International Monetary Fund. There are shortages of many goods and violence has flared up again.
Mr Maduro has accused the opposition of using violence and looting to create chaos and destabilise his government.
"I am more determined than ever to defend my country and my people against right-wing coup plotters," he said on Wednesday during a pro-government rally attended by tens of thousands of his supporters.
"I won't give in an inch," Mr Maduro added.
His term ends in 2019 and the next elections are not due until late 2018.
The opposition says the country can no longer cope with the chronic shortage of basic goods, medicine and a lack of investment.
Opposition leaders laid out their four key demands ahead of Wednesday's marches across Venezuela:
- Removal from office of Supreme Court justices who issued a ruling stripping the National Assembly of its powers (the ruling has since been revoked)
- General elections in 2017
- Creation of a "humanitarian channel" to allow medication to be imported to counter the severe shortages in Venezuela
- Release of all "political prisoners"
The government and its supporters blame "imperialist forces" led by the United States for the dismal state of the economy and say they are victims of an "economic war" being waged against them.