A judge in Spain has summoned international monitors who met with the armed Basque separatist movement ETA for questioning over the whereabouts of the group's fugitive members, a court source says.
Judge Ismael Moreno at the National Court in Madrid "summoned the six verifiers as witnesses", the source said, referring to the members of the International Verification Commission.
The commission on Friday announced it had verified that ETA had given up a cache of weapons as the first step towards disarmament.
It has been monitoring a ceasefire by ETA but is not recognised by the Spanish government.
The commission released a video filmed last month of masked ETA members presenting the weapons cache to two members of the commission in an undisclosed location in the Basque Country.
The Madrid judge summoned the six, including the commission's Sri Lankan spokesman Ram Manikkalingam, for questioning at 10am (2000 AEDT) on Sunday, said the court source, who asked not to be named.
The court will question them as witnesses as requested by the state prosecution service, in response to a case brought by Covite, an association for victims of ETA.
Covite said in a statement it had lodged a demand for the court to question the monitors to find out the identity of the ETA members they met "and any information that may be useful for the security forces to detain wanted criminals".
