(Recasts throughout, adds strike detail, Avianca suspension)
CARACAS/BARINAS, Venezuela, July 27 (Reuters) - Clashes between Venezuelan security forces and demonstrators have killed three people during the latest opposition-led strike to protest against an election on Sunday critics say will mark the end of democracy in the OPEC nation.
Many streets remained barricaded and deserted on Thursday, as the nationwide work stoppage entered its second day.
Plenty of rural areas and working-class urban neighborhoods were bustling, however, and the strike appeared less massively supported than a one-day shutdown last week. With Venezuela already brimming with shuttered stores and factories, amid a blistering four-year recession, the effectiveness of any strike can be hard to gauge.
Both of the latest stoppages were held to heap pressure on unpopular President Nicolas Maduro to scrap his plan for Sunday's vote for a Constituent Assembly, which will have power to rewrite the constitution and shut down the existing opposition-led legislature.
At least 106 people have died in anti-government unrest convulsing the South American country since April, when the opposition launched protests demanding free and fair elections to end nearly two decades of socialist rule.
(For graphics on Venezula's economic crisis and anti-government protests see: http://tmsnrt.rs/2pPJdRb and http://tmsnrt.rs/2ujuylf)
"People are working out of necessity," said coffee seller Jose Vazquez, 46, in Caracas though he had fewer customers than usual and there was little traffic on the streets around him.
In Barinas, home state of former Venezuelan leader Hugo Chavez, only about a third of businesses were closed according to a Reuters witness, as opposed to the opposition's formal estimate of 92 percent participation nationally.
"I am opposed to the government and I agree we must do everything we can to get out of this mess, but I depend on my work. If I don't work, my family does not eat," said Ramon Alvarez, a 45-year-old barber at his shop in Barinas.
Adversaries say the ruling Socialist Party wants to consolidate dictatorship with with Sunday's vote. There has been widespread international condemnation of the ballot, and the United States on Wednesday announced sanctions against 13 current and former officials for corruption, undermining democracy, and participating in repression.
Government officials and candidates for the Constituent Assembly were winding up campaigning on Thursday, with a rally in Caracas to be attended by Maduro.
The leftist leader has said the assembly is the only way to empower the people and bring peace to Venezuela.
The Venezuelan prosecutor's office said on Thursday that a 23-year-old man was killed in western Merida state and a 16-year-old boy died in the poor Caracas neighborhood of Petare during clashes on Wednesday.
That added to the previously announced death of a 30-year-old man, also in Merida, on the first day of the strike.
Nearly 180 people have been arrested during the strike so far, said local rights group Penal Forum. Since April, authorities have rounded up nearly 4,800 people, of whom 1,325 remain behind bars, the group said.
Further isolating Venezuela, Colombian airline Avianca followed some other international carriers in suspending all flights to the country on Friday, citing "operational and security limitations."
Voters on Sunday will choose 364 constitutional representatives distributed across municipalities and state capitals and another 181 "sectoral" candidates from demographic groups ranging from students to farmers and fisherman.
The opposition Democratic Unity coalition is boycotting the vote. They say the use of sectoral candidates, who had to collect signatures and file them to the government-leaning elections council, was a way to weed out anti-government aspirants.
Critics also note the lopsided representation of rural areas, where the Socialist Party has historically been strongest, at the expense of the opposition-leaning cities.
The country's least-populated state of Amazonas will elect eight representatives to the assembly while the capital of Caracas will choose only seven, according a document about the vote posted on the National Electoral Council's website.
State demographics agency INE data shows Amazonas having a population of 188,000 and the municipality of Caracas 2.1 million.
(Additional reporting by Brian Ellsworth, Anggy Polanco, Andrew Cawthorne; Writing by Andrew Cawthorne and Girish Gupta; Editing by W Simon and Tom Brown)