FIFA president Sepp Blatter played down concern about sluggish World Cup preparations on Thursday, though his deputy warned Curitiba must prove it can finalize work to remain a venue.

Blatter met visiting Brazilian President Dilma Rousseff at FIFA headquarters in Zurich and the pair both made positive noises about Brazil's ability to deliver come the big kick-off on June 12.

But FIFA secretary-general Valcke was somewhat more circumspect after Tuesday having warned Curitiba might be dropped as one of the 12 host cities for the tournament due to slack preparations.

With Rousseff insisting Brazil will come good in time, Blatter also sounded a reassuring note after their Swiss talks.

"Confidence reigns. We now still have several months to go and we still need to make a few small adjustments here and there," Blatter said, even if Valcke, visiting Rio, stressed that "issues" remained to resolve.

"I'm used to World Cups. There won't be any problem. In the end, everything will be fine in Brazil," Blatter predicted.

FIFA initially set a firm December 31 deadline for all 12 of Brazil's venues to be completed but had to scrap that date with half of the stadiums still requiring work, including Sao Paulo, which will host the opening match on June 12 between the hosts and Croatia.

Rousseff earlier this month countered criticism from Blatter over Brazil's tardy preparations by insisting the country will host the "Cup of Cups".

On Thursday, she reiterated that pledge.

"The Brazilian government will do everything, and the stadiums will be ready...We will do everything to ensure that this will be the globe's most beautiful World Cup ever," the Brazilian leader said in Switzerland, where she will attend the World Economic Forum in the Alpine resort of Davos.

In rio, Valcke meanwhile confirmed February 18 as the deadline for Curitiba to prove it has responded to his threat to drop the venue.

Valcke told a press conference at Rio's Maracana arena that FIFA now expected stadium delivery in late April or early May, "which is very late".

Valcke said it would be a major challenge to change the plan for four games in Curitiba, saying he would prefer to see the stadium completed at the last minute rather than to resort to a Plan B.

"Curitiba will not be excluded from the World Cup, I am absolutely certain," insisted Jose Maria Martin, president of Brazil's Football Confederation (CBF).

But Valcke stressed Curitiba remained a challenge.

He told reporters: "There is no easy solution -- the best one for Brazil is to make sure we can organize these four games in Curitiba," said Valcke, who angered Brazil last year in suggesting the hosts needed a "kick up the backside" to speed up preparations.

"We will look at what's happening in the stadium every minute of the day. There are issues -- as long as it's not finished there will always be issues," said Valcke.

Also Thursday, former Brazil star Rivaldo, a World Cup winner in 2002 and 1999 FIFA player of the year, said it would be "a shame for Brazil to stage the World Cup when the country "needs to build schools, hospitals or prisons rather than stadiums."

Echoing his criticism, World Cup opponents announced new protests in 36 Brazilian cities for Saturday with the slogan "there won't be a Cup."

Deputy Brazilian sports minister Luis Fernandes said Brazil would do everything it could to ensure Curitiba is kept as a venue.

He vowed to overhaul management of the construction team there and to determine if more workers could not be drafted to add an extra daily shift to speed things up.

"We believe once these measures are implemented we can guarantee delivery of the stadium," said Fernandes.

Fernandes pointed out there had been serious doubts over the northern city of Recife's readiness for last June's Confederations Cup -- a World Cup dress rehearsal -- but ultimately had delivered.

"Concern was voiced -- and yet the stadium was delivered."