(Adds day of mourning, updates count of dead and injured, crash details)
By Hugh Bronstein and Walter Bianchi
BUENOS AIRES, Dec 14 (Reuters) - A bus carrying Argentine border patrol officers blew a tire and tumbled from a bridge into a dry river bed in the northern province of Salta on Monday, killing 43 and injuring eight, authorities said.
The vehicle was part of a three-bus convoy carrying officers of Argentina's gendarmerie, which patrols the country's borders. Salta borders Bolivia, Chile and Paraguay.
Border security has become a hot issue in Argentina as the country has emerged as part of a route used for smuggling Andean cocaine to Europe and for human traffickers sending Syrian refugees through the Western Hemisphere.
"Forty three gendarmes lost their lives here today. Eight more were injured, one critically," Salta Governor Juan Manuel Urtubey told reporters at the scene. "We are still working to recover bodies from inside the bus."
Passengers on the other two buses in the convoy were the first to venture into the ravine to try to save those trapped in the wreckage. TV images showed the bus completely upside down at the bottom of a steep slope covered in lush green vegetation.
"It appears that one of the tires of the bus blew out, unfortunately just a few meters ahead of the bridge. It went over the guardrail," Argentine security chief Patricia Bullrich told reporters.
President Mauricio Macri, elected last month on a platform that included improving Argentina's rural roads, sent his condolences to families of the victims of the crash and declared a national day of mourning.
"We need to improve our highways so these things don't keep happening," he told reporters on the sidelines of a news conference in Buenos Aires province. (Writing by Hugh Bronstein; Editing by Bernadette Baum and Alan Crosby)
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