Two fans were shot to death on their way to a test event Sunday at a World Cup stadium in northeastern Brazil, just two months before the venue hosts matches in the Confederations Cup.
The fans were killed about 5 kilometres from the Arena Castelao in the city of Fortaleza, one of the six venues hosting matches in the Confederations Cup in June and one of the 12 getting ready for next year's World Cup.
"We lament what happened,'' said Tiago Paes, a local World Cup organizing committee member who was at the test event in Fortaleza.
"But there is work being done by the police and the army in many areas of security, so we are not concerned with that for the Confederations Cup.''
The official in charge of Ceara state's World Cup preparations said that the deaths were not connected to the test event at the Arena Castelao.
"I'm extremely sad,'' said Ferruccio Feitosa.
"But the fans were killed away from the stadium.''
The deaths came before a match between local rivals Ceara and Fortaleza, which was used by local organisers to evaluate the venue.
Police said the victims, wearing Ceara jerseys, were shot in the head after being confronted by Fortaleza supporters at a plaza. Witnesses told authorities the men had just left a van and were getting ready to walk from the plaza to the stadium when two rival fans on a motorcycle opened fire at them.
It wasn't clear whether there was a confrontation before the shots were fired.
Authorities later detained a man suspected of being involved in the shooting. He was found near the crime scene on a motorcycle and allegedly was carrying a gun. His identity was not immediately released.
Police said more than 180 people were detained for vandalism and disorderly conduct before Sunday's match at the Arena Castelao, which was the first World Cup stadium to be delivered by Brazilian organisers.
It was completed in December and already has hosted nearly 20 test events, according to local organisers. Another 10 events will take place before it hosts its three Confederations Cup matches in June. A Paul McCartney concert scheduled for May will also serve to evaluate the facility.
The Arena Castelao will host Brazil vs. Mexico, Nigeria vs. Spain and a semi-final match in the warm-up World Cup tournament.
Despite the fan violence, World Cup organisers said they were satisfied with Sunday's test, which included an evaluation of the stadium's sound and television system, as well as crowd management and cleaning services.
"It went well in all areas, although adjustments are always necessary,'' Paes said after Ceara beat Fortaleza 1-0 in front of more than 15,000 people.
"It went on as planned.''
Also Sunday, officials announced that construction work was completed at the Arena Pernambuco in Recife, which will also host three Confederations Cup matches. The inauguration game at the venue is scheduled for May 22.
FIFA wanted all six Confederations Cup venues ready last December, but it had to extend its deadline because of the construction delays. Football's governing body has already said that it won't make similar exceptions for the World Cup. It wants all venues ready for the tournament by the end of this year.