There have been major delays at airports across Brazil after more than 8,000 federal police officers began an indefinite strike for higher pay.

Foreign passengers arriving at Sao Paulo airport have had to queue for up to three hours for immigration checks.

Ordinary police work is not affected, but the stoppage is likely to affect investigations into corruption and organised crime.

The police want an 85% pay rise, which the government says it cannot afford.

Strike organisers said most of the force was expected to observe the stoppage, although the federal police will still deal with emergencies.

The strike is the first major challenge to President Luiz Inacio Lula da Silva's administration over public sector pay and could become a test of nerve, says the BBC's Steve Kingstone in Sao Paulo.

Sympathy

The federal force, whose work is roughly similar to that of the FBI in the United States, is responsible for immigration services at Brazil's airports and other borders.

The officers carry out the photographing and fingerprinting of American visitors - a move implemented in response to a similar US decision.

Their demands amount to an 85% increase in their salaries, which start at about $1,500 a month.

On Tuesday, the Ministry of Justice issued a statement saying it had some sympathy with the police but was unable to grant a pay rise without a further change in the law, adding that no other public employees had received a similar increase.

Our correspondent says this suggests that the government wants to keep public spending tight as part of a disciplined economic policy that has taken some observers by surprise.

The police have agreed to maintain basic staffing and cover for emergencies but insist they will stay on strike indefinitely.