Spanish police are reported to be hunting five Moroccan Muslim militants suspected of helping plant the bombs that killed 201 people in Madrid last week.
The five are part of a group of eight main Moroccan suspects, three of whom are already in custody for alleged involvement in the bombings that injured over 1,500 people.
One of the three Moroccans in custody has been named as Jamal Zougam. Police sources said bomb survivors had identified him from photographs as having been at the crime scene but said they were treating witness reports cautiously.
Legal sources said the bombers are believed to have left the country. However, police sources said no international arrest warrants had been issued. Investigators were also examining the remains of one of the dead from Thursday's train blasts as a potential bomber.
The Moroccan line of investigation first emerged at the weekend when police arrested five suspects - three Moroccans and two Indians - in their first breakthrough. The Indians are not believed central to the case.
El Paisnewspaper said Zougam had connections with some of those arrested for last May's bombings in Casablanca that killed 45 people, including 12 suicide bombers.
As well as the Moroccans, police were also looking for Islamists of other nationalities who may have played a part in the attack, media and sources said. They are suspected of being loosely related to al-Qaeda.
Morocco sent a security team to Madrid to help with investigations on Sunday. Moroccan officials have questioned whether there is any link between the Madrid bombers and the radicals who staged the Casablanca bombings. Spanish Foreign Minister Ms Ana Palacio attended an ecumenical memorial service for victims in the Moroccan capital Rabat today.
Incoming Socialist leader Jose Luis Rodriguez Zapatero said his first official visit, after taking office in around a month, would be to Morocco as is traditional for Spanish leaders.
National flags decked with black ribbons flew from balconies in Madrid as the nation mourned its worst ever bomb attack. Among the 1,500 wounded, 220 remained in hospital, many fighting for their lives. A woman (45) died today, becoming the 201st victim.
Thursday's bombs, which authorities initially blamed on armed Basque separatists ETA, revived popular anger at Prime Minister Jose Maria Aznar's support for the US-led Iraq war.
Spain's prime minister-elect, Mr Zapatero, said yesterday he would probably pull Madrid's troops out of the "disastrous" occupation unless the United Nations takes charge there by mid-year, an unlikely event.