One person was shot dead and 15 wounded on Saturday during a demonstration against President Hugo Chavez in Caracas, said Vice-President Jose Vicente Rangel.
It is not clear who was behind the shootings
Three of those injured were National Guard soldiers whose patrol was ambushed as they took part in a big security operation to try to keep the peace at the rally, which was being held in a Chavez stronghold.
Chavez supporters and opponents have blamed each other for the violence.
The fresh blood was spilled just 24 hours after a 19-point accord was brokered between Venezuela's warring factions which looked set to see a referendum held on Mr Chavez's rule in a few months' time.
Panic and confusion
The man shot and killed in the gunfire was named as Modesto Martinez, 48, by the director of the police department, Lazaro Forero.
Among those injured was a motorcyclist shot in the neck and a person shot in the chest.
There were scenes of panic as demonstrators threw themselves to the ground or tried to flee through the labyrinthine alleyways of Catia, a poor, strongly pro-Chavez district of the capital.
The small streets also impeded the operations of between 2,000 and 4,000 police deployed to keep order.
'Conquest of western Caracas'
Some witnesses described shots coming from side alleys, where groups of Chavez supporters had gathered to shout insults at protestors.
Small bands of self-proclaimed pro-government street fighters had also warned Venezuelans not to attend the demonstration, predicting violence.
But the general of the National Guard, Marcos Rojas, accused the opposition group Red Flag of instigating the violence.
Ruling party lawmakers have also accused the rally organisers, the Democratic Action party, of deliberately provoking the clashes by holding the rally in Catia, which houses more than half of the city's four million inhabitants.
Chavez supporters stood on the sidelines to jeer at demonstrators
The protest had been dubbed "the conquest of western Caracas" by the organisers.
It is not clear whether this latest flare-up will derail the planned formal signing of Friday's pact between the government and opposition next week.
The plan was finally agreed after six months of negotiations brokered by Cesar Gaviria, secretary-general of the Organization of American States.
Referendum on Chavez
A key point is Mr Chavez's agreement to submit to a referendum on his rule - long demanded by the opposition but outlawed by the constitution until at least half-way through his six-year term.
The two sides are said to have agreed that the referendum will go ahead after that date - which falls on 19 August - as long as government opponents gather signatures from 20% of the electorate as constitutionally required.
Another hurdle that remains is the government insistence that the National Assembly first select a new National Electoral Commission to verify the referendum petition.
Lawmakers are still haggling over which candidates should make up the new commission.
Both sides also agreed to:
- Respect democracy
- Disarm the civilian population, after the deaths of at least 50 people and wounding of several hundred more in clashes over that last 18 months.
A strike called in December by Chavez opponents struck a severe blow at the economy before finally petering out in January.