A tragedy struck Brazil's fledgling space program Friday when a rocket exploded on the launch pad during pre-flight tests, killing more than a dozen people, destroying the booster and ending the nation's third attempt to put a satellite in orbit over the past few years.

Reports from the Alcantara launch base on Brazil's northeast coast on fatalities and damages remain unclear, but the Globo News organization said local defense officials indicate at least 16 people were killed during the explosion. Reuters reported that 19 were dead and 20 more injured.

Officially, the Brazilian defense ministry says the explosion "caused a substantial number of deaths" of civilian workers at the launch pad. An investigation into the cause of the accident was immediately launched, the ministry said in a statement Friday afternoon.

The explosion of the third VLS rocket apparently was at about 1:30 p.m. local time at the Alcantara launch center, located in northeastern Brazil on the Atlantic coast near the equator.

The booster was being readied for an upcoming launch of a pair of small satellites into Earth orbit, an achievement Brazil has been actively seeking for almost a decade.

Two previous flights of the VLS rocket ended in failure in 1997 and 1999. Both were remotely destroyed shortly after liftoff and neither incident resulted in deaths.