CARACAS, July 3 (Reuters) - Venezuela’s unofficial exchange rate broke through 500 bolivars per dollar on Friday, according to a widely used website, as the socialist-run country’s currency control system struggles to meet keen demand for greenbacks.

The rate weakened to 501.21 bolivars per dollar on Friday, clocking a 65 percent tumble this year, according to DolarToday, which says it publishes the figure based on currency trades along the Colombian border.

A severe recession and a fall in oil prices have slammed the OPEC nation’s ability to provide dollars through a complex three-tiered currency control system.

Critics say President Nicolas Maduro has failed to take urgent measures to ease or phase out these controls, which have crimped imports and caused severe shortages of goods ranging from milk to medicines and spare parts.

“As long as they don’t make the adjustments the economy needs, the rate will continue to increase,” said Asdrubal Oliveros of Caracas-based consultancy Ecoanalitica.

Maduro says DolarToday is part of a broader right-wing campaign to sabotage his two-year government via an “economic war.” He has ruled out dismantling the controls, saying that would benefit the wealthy.

The currency slide, as well as roaring inflation, has slammed Venezuelans’ purchasing power. The monthly minimum wage is now equivalent to around $15 on the unofficial exchange rate.

“The dollar has already reached 500 bolivars and the paralyzed government is still awaiting a miracle,” said Jose Guerra, an opposition economist running for a seat in parliament in December’s election. (Reporting by Alexandra Ulmer, Eyanir Chinea and Girish Gupta)