Spain's government is facing intense pressure over its handling of a migrant disaster in Melilla this summer.
At least 23 migrants died in a "stampede" while trying to cross the Moroccan border to the Spanish enclave in northern Africa on June 24.
Independent experts appointed by the UN Human Rights Council have put the death toll as high as 37.
A recent BBC documentary has claimed that at least one person died in an area controlled by Spanish forces, who allegedly failed to prevent the deaths of dozens of African migrants.
"Other lifeless bodies were pulled out [of Spanish territory] by Moroccan security forces," according to the BBC report.
Spain's interior minister Fernando Grande-Marlaska has maintained that there were "no deaths on Spanish territory" during the tragedy.
The Spanish government has also condemned the BBC, saying it is "disappointing and surprising" that "accusations" were made "without evidence".
Spain had previously stated that "50 civilian guards were injured" during a "violent attack on the border" on June 24.
Nearly 2,000 migrants -- many from Sudan -- had tried to cross the border fence into the European Union in the incident.
Spanish border police fired teargas canisters and rubber bullets in an attempt to drive the migrants back.
UN experts have accused both Moroccan and Spanish authorities of "an excessive and lethal use of force" and an "alarming" lack of accountability.
Amnesty International has joined calls for a thorough, transparent investigation into the tragedy -- the worst ever of its kind at Melilla.
Spain's Ombudsman, who is investigating the tragedy along with the public prosecutor's office, said in mid-October that Spain had failed to respect the "legal guarantees" of migrants.
Opposition MPs have called for Grande-Marlaska’s resignation, accusing him of withholding evidence, namely security footage, from investigators.
Speaking to reporters on Monday, Grande-Marlaska reiterated that Spanish security forces had acted "legally, proportionately, and (according to) necessity".
Madrid and Rabat signed a bilateral agreement in April on migration and border controls at Melilla and another Spanish enclave, Ceuta.
Over two days in March, more than 3,500 people tried to scale the border fence that surrounds Melilla. Nearly 1,000 successfully crossed into the North African enclave, according to Spanish authorities.