Concerns over Brazil's readiness to host next summer's World Cup have been upgraded after the country's sports minister admitted he was worried about delays to the construction of new stadiums.

Aldo Rebelo warned that the venues will not be delivered on time if construction is not accelerated.

It was recently revealed that only one of the six stadiums - the venue for the opening match in Sao Paulo - is on schedule to be completed by the end of this year. That is the deadline given by Fifa for the venues to be completed.

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While the stadium in Sao Paulo is 84 per cent complete, the other five in Manaus, Curitiba, Cuiaba, Porto Alegre and Natal are from 71 per cent to 79 per cent ready.

"This must be seen as a warning. We cannot keep on the same rhythm, or we will not deliver them on time," said Rebelo.

"It is possible to intensify. We are able to meet the deadlines, but it should be noted that it will require us to speed up the construction."

Rebelo warned that no extra funding to speed the building process would be forthcoming from the government.

"There will be no budget increase, because, for example, instead of paying 10 workers during two months, you can pay 20 to work for 30 days," Rebelo explained.

Throwing more money at the tournament would be hugely unpopular, with this summer's Confederations Cup, seen as a test event for next year's tournament, overshadowed by protests about corruption and overspending.

However, that may be unavoidable with Fifa warning during the Confederations Cup that there is no 'Plan B' if Brazil fail to be ready.

The World Cup will be hosted across a total of 12 venues in Brazil with the tournament scheduled to begin on 12 June.

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