The killing Wednesday came on the first of a two-day general strike called by opponents of President Nicolas Maduro.
But some 70 percent of Venezuelans are opposed to the Constituent Assembly, according to polling firm Datanalisis.
Maduro said the role of the new body will be to "perfect" the current constitution and promises that the changes will help the oil-rich nation climb out of its crippling economic crisis.
The National Assembly parliament has been in the hands of the opposition since December 2015, when voters democratically elected a majority of the candidates.
The U.S. announced new sanctions on senior Venezuelan government officials. Through the U.S. Treasury Department, all assets under U.S. jurisdiction held by the 13 individuals have been frozen, and U.S. citizens are now prohibited from dealing with them.
Among those sanctioned on Wednesday were: national elections director Tibisay Lucena, PDVSA finance vice president Simon Zerpa and former PDVSA executive Erik Malpica, as well as prominent former ministers Iris Varela and Elias Jaua.
Colombia's flagship airline is suspending all flights to neighboring Venezuela, citing security concerns. In its statement, Avianca noted that Venezuela now is failing to meet global standards and needs to improve its airport infrastructure.
Quite a few countries have shaky economies, with double-digit unemployment, crumbling treasuries and even food shortages.
Last week, Trump said Washington "will not stand by as Venezuela crumbles".
With the approach of controversial elections on Sunday of a 545-seat Constituent Assembly to rewrite the constitution, the opposition and the Maduro government skirmished in the streets. The crisis will worsen.
The most serious of the potential future steps would be financial sanctions that would halt dollar payments for the country's oil, starving the government of hard currency, or a total ban on oil imports to the United States, Venezuela's biggest customer.
Venezuela's opposition, bolstered by an unofficial vote on July 16 that saw a third of the electorate reject Maduro's plan, has called for a boycott of Sunday's vote. And in that sense, it will be rigged to be pro-government, pro-Maduro.
Speculation that Havana could play a role in potential worldwide mediation had been sparked by a recent visit to the island by President Juan Manuel Santos of Colombia.
Foes have said that would institutionalize dictatorship by the ruling Socialist Party.
Human rights organizations and foreign governments criticized Lopez's detention as politically motivated.
He spoke Wednesday at a ceremony marking the anniversary of a failed barracks uprising that is considered the beginning of Fidel Castro's revolution.
Although both decisions were overturned within days, opposition leaders continue to lead the protests aimed at toppling President Nicolas Maduro, removing the members of the Supreme Court, restoration of local and regional elections, and release of political prisoners. Bolivia, Nicaragua and Cuba have all lent their backing to Caracas in the build-up to Sunday's vote.
"We're on the brink of their trying to annihilate the republic that you swore to defend", he says.
NWS: rainy weekend likely, with possible severe thunderstorms this evening
TUESDAY NIGHT: Partly cloudy skies and mild temperatures will be around, with a low temperature of 65 degrees. SATURDAY: Lower 90s return for Saturday afternoon, with the chance for a few rain showers and thunderstorms.