Moroccan authorities gave the information to Judge Baltasar Garzon, Spain's leading "al-Qaida expert", in Rabat earlier this month, El Pais said on Sunday, citing a person who was present at the meeting.
Spain and Morocco have been cooperating closely in security matters since the 11 March train bombings that killed 191 people and injured 1900 in Madrid.
Investigators blame the attacks on individuals acting in the name of al-Qaida, and a Spanish judge has formally accused 24 people of involvement, most of whom are Moroccan.
Authorities in Rabat told Garzon they knew of 600 Moroccan nationals who had allegedly been at al Qaida camps, but only knew the whereabouts of 200 of them, El Pais said.
Garzon has been investigating suspected al-Qaida members in Spain for years and has ordered 15 alleged members of the network to face trial. He was in Morocco to question several individuals who have been imprisoned.
Incidents in May last year, in Casablanca, shocked the kingdom which had prided itself of being a haven of stability in the Arab world.