(Adds details from Caracas rallies)
By Eyanir Chinea and Andrew Cawthorne
CARACAS, Feb 18 (Reuters) - Rival rallies convulsed Caracas on Tuesday and a protester struck by a vehicle in eastern Venezuela died, the fourth fatality from political unrest over the past week against President Nicolas Maduro's government.
Residents said the 17-year-old student was hit during a demonstration against the OPEC member nation's socialist government late on Monday in the coastal town of Carupano.
That added to three fatal shootings last week in Caracas.
Student-led protests have multiplied this month across the South American nation of 29 million people in the biggest challenge to Maduro since his election last year.
The demonstrators are demanding Maduro's resignation and expressing a litany of complaints from inflation and crime to corruption and product shortages.
"The country's in an unsustainable state," said filmmaker Jose Sahagun, 47, wearing white like many among several thousand protesters at a gathering in east Caracas to show support for wanted opposition leader Leopoldo Lopez.
"The government's mask has fallen off. This man (Maduro) has held power for 10 months and the deterioration has been fast."
Protest numbers, though, are small compared to mass movements in places such as Brazil, Ukraine and the Middle East, with little sign of Venezuelans joining en masse in the hundreds of thousands seen on the streets a decade ago.
Nor has there been any evidence Venezuela's military might turn against Maduro, the 51-year-old successor to Hugo Chavez.
"The armed forces will always be on the side of justice and development of the fatherland," Defense Minister Carmen Melendez said. "Every act of violence takes us back to intolerance."
Several thousand oil workers and Maduro supporters, clad in the red of the ruling Socialist Party, held their own demonstration on Tuesday, music blaring in a party atmosphere.
"Comrade President Nicolas Maduro can count on the working class," said oil union leader Wills Rangel.
In a nation split largely down the middle on political lines, 'Chavistas' have stayed loyal to Maduro despite unflattering comparisons with his famously charismatic predecessor. Many Venezuelans fear the loss of popular, oil-funded welfare programs should the socialist lose power.
"Chavez lives, the fight goes on," Maduro backers chanted.
'HOW LONG THE HATE?'
An opposition legislator and anti-government activists alleged that a government supporter had hit the dead student in Carupano, Jose Ernesto Mendez, but there was no independent confirmation or any response from authorities.
"For how long will the hate go on?" Cesar Rincones, a legislator of the opposition Democratic Action party, tweeted.
Residents said three other demonstrators were injured in the melee in Carupano, in Sucre state. One was gravely hurt.
In Caracas, security forces in anti-riot gear patrolled the streets with water cannons. Police told opposition supporters they would not be allowed to march beyond a small area of the city's eastern district where they were gathered.
Many residents stayed home, fearing more trouble after the daily clashes that have erupted since last Wednesday's fatalities in the capital. Schools were mostly closed.
Hardline opposition leader Lopez, 42, had called supporters to join him on Tuesday as he prepared to give himself up to authorities who have issued an arrest warrant for him on charges of murder and terrorism tied to the recent violence.
The U.S.-educated economist Lopez, who has a Masters from Harvard University and is a distant relative of Venezuelan independence hero Simon Bolivar, was spearheading protests but has disappeared from public view since Wednesday.
The government is calling him "the face of fascism."
"I will show my face. I have nothing to fear or hide," Lopez said in a stream of defiant tweets.
Maduro's government accuses opponents backed by Washington, of seeking to promote a coup against him, similar to a botched attempt against Chavez in 2002 when he was ousted for 36 hours.
The burly 51-year-old former bus driver and union activist this week expelled three U.S. diplomats accused of recruiting students for the protests. Washington called that "baseless."
Prices of Venezuela's highly traded global bonds , which fluctuate sharply on political tension, are at 18-month lows.
Complaints about acts of violence by both sides have piled up over six consecutive days of confrontations between police and demonstrators. Only 13 students were still reportedly detained after nearly 100 arrests in the past week.
Opposition activists say some of the detained students have been tortured, but Maduro says police have been restrained in the face of provocation and attacks.
He has, however, publicly criticized the Sebin national intelligence service for having agents in the street and replaced its head on Tuesday. (Additional reporting by Jaczo Gomez, Deisy Buitrago and Daniel Wallis; Editing by Daniel Wallis and James Dalgleish)