SAO PAULO, Brazil — A radar failure over the Amazon forced Brazil to turn back or ground a string of international flights Saturday, deepening a national aviation crisis just hours after the president unveiled safety measures prompted by the country’s deadliest air disaster.

Further shaking Brazilians’ confidence, authorities said they had mistaken a piece of the fuselage from Tuesday’s accident for the flight recorder and sent it to a laboratory for analysis.

The radar outage from midnight to 2:30 a.m., which Brazilian media said was apparently caused by an electrical problem, forced numerous planes heading to Brazil to return to their points of origin and make unscheduled landings at airports from Puerto Rico to Chile.

“This is total chaos here. I have never seen anything like it and it makes me feel very unsafe,” said Eli Rocha, 52, of Oklahoma City, who was trying to board a flight to Dallas on Saturday at Sao Paulo’s international airport. The flight was crowded with weary Americans arriving on other delayed or diverted flights.

The confusion followed a nationally televised speech by President Luiz Inacio Lula da Silva, who tried to calm the nation Friday night by announcing new safety measures and saying authorities will build a new airport in Sao Paulo, where an Airbus A320 operated by TAM Airlines crashed, killing 191 people.

All 187 people aboard and at least four on the ground died when the jetliner raced down the runway, skipped over a crowded highway and exploded in a fireball that was still smoldering three days later.