Spain says it will declassify intelligence documents relating to last week's bomb attacks on commuter trains in the capital, Madrid.
The decision was made Thursday, by Spain's outgoing cabinet, which was voted out of power in Sunday's general elections, three days after the bombings.
The government initially blamed the attacks on the Basque separatist group ETA. But authorities are now investigating whether the al-Qaida terrorist network was involved.
Spanish news media say authorities have arrested four more suspects in connection with last Thursday's bombings, which killed more than 200 people and wounded 1500 others.
The reports say the suspects are of North African origin.
Three were arrested in the Madrid suburb of Alcala de Henares, where authorities believe the bombs were planted on commuter trains. The fourth suspect was arrested in the north of the country.
The reported number of suspects in custody is now nine.
Five people: three Moroccans and two Indians, were arrested in the days immediately following the March 11th bombings. They are scheduled to appear before Spain's highest criminal court Thursday, where a judge must decide whether to charge them or release them.