The national Globo network's website cited police sources in their report that the two young men, fans of visiting team Ceara, were shot in the head from a passing vehicle allegedly carrying two Fortaleza supporters.
The Folha de Sao Paulo newspaper said Ceara fans started a fight by throwing stones at Fortaleza supporters, which sparked the shooting.
They said an unidentified man had been arrested in connection with the incident which occurred about five kilometres from the Arena Castelao and police carried out severe security checks at vantage points close to the stadium.
Ceara beat bitter rivals Fortaleza 1-0 in their Cearense state championship match in the Atlantic coast city, where the stadium had its first test for Confederations Cup.
The Confederations Cup, to be played by eight nations from June 15-30, is a dress rehearsal for the World Cup finals a year later in Brazil.
Folha quoted World Cup local organising committee official Tiago Paes as saying the incident was not directly related to Sunday's match, which went smoothly with a crowd of about 15,000.
"There is a lot of training work by the military police, civil police and even the army. We don't have such concerns for the Confederations Cup," Paes said.
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