In Rio de Janeiro, striking federal police officers wore t-shirts that read "SOS federal police"

Federal police in Brazil have gone on strike over pay, and threatened to continue their protest during the football World Cup next month.

A spokesman for the striking officers, Renato Deslandes, told the BBC that "at least 40%" of the force took part.

He said their protest would continue if the government did not increase pay in line with inflation.

The 24-hour walkout took place across Brazil, including some of the cities that will host the football tournament.

A similar police strike last month in the north-eastern state of Bahia forced the authorities to deploy federal troops to restore order on the streets.

On Wednesday, there were protests in Rio de Janeiro, Brasilia and Fortaleza, among other cities. There was no independent estimate of the number of police involved in the strike.

In Rio, some 50 striking officers covered their mouths with red scarves and wore t-shirts that read "SOS federal police".

The World Cup will be hosted in 12 cities, including Rio, from 12 June.

They stood next to a life-sized inflatable white elephant that symbolised the government spending and the high cost of hosting the World Cup in Brazil.

"Federal agents are the only category of workers whose salary has been frozen in the last five years," Renato Deslandes, Director of Communications for the National Federation of Federal Police Officers, told the BBC.

"We are not looking for a real salary increase, but a re-adjustment in accordance with inflation during those five years," he said.

A surge in food prices pushed inflation to 6.15% in the 12 months ending in March.

Mr Deslandes said police salaries were now worth 35% less than in 2009.

He added they would "continue striking in the coming weeks and during the World Cup if the government doesn't raise pay in line with inflation".

The police are paid between 7,500 and 12,800 reais ($3,200-5,800; £2,000-3,400) a month before tax and social security contributions, the AFP news agency reported.

Last month, thousands of soldiers were deployed to Bahia to maintain order after police went on strike for two days over pay.

State officials said 39 people were killed in and around the state capital, Salvador, during the walkout - a much higher figure than normal - and shops were also looted.