Caracas (AFP) - Thousands of Venezuelans crossed into Colombia to buy food and medicine after their government partially reopened the border following a messy crackdown on what it called currency hoarders.

The border with Brazil was also partially reopened, officials in Brasilia said.

"Thank God the border is open again," 29-year-old Christian Sanchez told AFP.

"A lot of people have come to shop on the other side because we can't find food, diapers for our babies, medicine," he said.

Sanchez was preparing to enter a pedestrian crossing over the Simon Bolivar Bridge linking the cities of San Antonio in Venezuela and Cucuta, Colombia.

But while foot traffic was permitted, trucks carrying needed goods remained blocked.

Venezuela also reopened its main border crossing with Brazil after talks between officials at the Brazilian embassy and Venezuela's foreign ministry, officials in Brasilia said in a statement.

The crossing is open for pedestrians, but only within limited hours for vehicles.

Local press reported that some 200 Brazilians, mostly local tourists, were prevented from returning home when Venezuela closed the border.

President Nicolas Maduro had ordered the borders with Colombia and Brazil closed on December 12 as part of a currency reform that involved removing the 100-bolivar note from circulation.

He alleged that "mafias" abroad were hoarding the banknotes to suffocate the Venezuelan economy.

On Tuesday, he also accused the United States of causing the cash crisis by infiltrating his government.

"Is it not the case that the gringos have bought key people in key positions in order to harm the people?" he said without identifying which institutions he believes to have been affected. "I think so."

- Dire crisis -

Looting and clashes broke out over the weekend as many people were left without cash. At least three people were reported killed and around 300 arrested.

The state of Bolivar was hardest hit by the unrest. A curfew has been in force there since Saturday, and more than 3,000 troops are patrolling the streets.

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Maduro eventually reversed course, saying the currency will remain legal tender until January 2 while new, higher denomination bills are printed and circulated.

Late on Monday, he and Colombian President Juan Manuel Santos spoke by telephone and agreed to reopen the border "progressively," according to Venezuelan information minister Ernesto Villegas.

While visiting the border town of Cucuta on Tuesday, Santos said in a televised speech that better cooperation "on both sides" was needed to crack down on contraband.

Venezuela is in the grip of a dire economic crisis spurred by low prices for oil -- the country's main export.

It is in its third year of recession and suffers the highest inflation in the world, which the IMF forecast could hit 475 percent this year.

Maduro blames outside forces -- frequently evoking a US "plot" -- for the severe downturn. But analysts say currency controls and government policies have aggravated the situation.

With the Colombian border seen as a lifeline for many Venezuelans struggling to make ends meet, long lines formed hours ahead of its reopening.

Marta Cardenas, a 51-year-old Colombian living in Venezuela, said the reopening was a "breath of fresh air" amid mounting daily problems, made worse with the shortage of cash.