An indefinite national strike in Venezuela is beginning to affect oil production in the world's fifth largest oil exporter.

Protesters are demanding a referendum

President Hugo Chavez conceded for the first time on Wednesday that the strike was hitting oil shipments, the French news agency AFP reported.

His acknowledgement came as thousands of protesters took to the streets of the capital, Caracas, on the third consecutive day of the anti-government stoppage.

Labour unions and business federations called the indefinite stoppage to demand a referendum on whether President Chavez should remain in office.

The government has dismissed union claims that the stoppage has been a success, saying the majority of Venezuelans have gone to work.

'Evil goals'

Analysts say the key to whether a long-term stoppage will really hit home is what happens within the oil industry, which provides half the government's revenue.

They won't achieve their evil goals of destabilising the country and stealing Venezuelans' Christmas

President Chavez

Managers at the state-run oil company PDVSA said an overwhelming majority of white-collar workers were supporting the strike.

Oil tanker loadings at some of Venezuela's ports were delayed on Wednesday, and striking workers said the problem could soon spread to the refineries.

"Are they causing problems? Are they causing delays? Surely they are, but they won't achieve their evil goals of destabilising the country and stealing Venezuelans' Christmas," Mr Chavez said in a statement.

Talks hope

Protesters, banging on pots and waving flags, gathered outside the offices of the state-owned oil company, PDVSA.

Opponents accuse Chavez of economic mismanagement

This was the site of disturbances on Tuesday, when national guard troops fired tear gas at thousands of demonstrators.

Correspondents say Wednesday's rally has been peaceful.

Strike leaders have suggested they are ready to resume talks - mediated by the American Organization of States - with the government.

Mr Chavez's supporters have also taken to the streets, but there have been no clashes between the two groups as on previous occasions.

On Wednesday, Pope John Paul II called for calm in Venezuela, in remarks made in Spanish during his weekly public address.

Twenty thousand members of the national guard have been deployed to avoid a repeat of violence which erupted at an April strike, when 19 people died in clashes between pro and anti-Chavez groups.

The street violence led to a short-lived coup, which saw President Chavez ousted for 48 hours and then re-instated by the military.