Morocco has warned Spain that it has lost track of hundreds of Moroccans who trained in al-Qaeda camps, a Spanish newspaper has reported.
The whereabouts of some 400 Moroccan fighters is "unknown"
Moroccan authorities reportedly told Spanish judge Baltasar Garzon that some 600 Moroccans had trained in camps in Afghanistan, Bosnia or Chechnya.
But they warned the whereabouts of 400 were unknown, El Pais reported.
Most of the 20 people provisionally charged with involvement in the 11 March bombings in Madrid are Moroccan.
Morocco suffered attacks on its own soil in May 2003, when co-ordinated bombings in Casablanca killed 45 people.
El Pais cited as its source someone who attended the meeting between Mr Garzon - a leading al-Qaeda expert and anti-terrorism investigator in Spain - and Moroccan officials in early July.
Papers found in al-Qaeda premises had allowed Moroccan authorities to compile lists of suspected nationals training in al-Qaeda camps, El Pais said.
Spanish Interior Minister Jose Antonio Alonso would not confirm the report but said Spanish authorities were in constant contact with their Moroccan counterparts.
The report appears to echo warnings given by Mr Garzon to a parliamentary commission investigating the 11 March bombings earlier in July.
He said there were dozens of al-Qaeda cells in Morocco capable of staging attacks in Europe.
Morocco increased co-operation with Spain following the Madrid attacks, in which 191 people were killed and some 1,900 injured.
The Moroccan authorities have arrested about 2,000 people in cases linked to militant activity since the suicide attacks in Casablanca, and the country has been praised by the US for its efforts to clamp down on terrorism.
However, human rights groups have said that the anti-terror measures have eroded human rights and that suspected Islamists have been tortured by security agents.