Armed Basque separatist group ETA will pledge to put its weapons 'beyond use', Spanish newspaper El Pais reports.
The report comes ahead of first news conference from the international commission set up in 2011 to monitor ETA's ceasefire. The group will report their findings this afternoon.
ETA is responsible for the death of 800 people over four decades. The group, which seeks independence for the Basque region of northwestern Spain and southern France, publicly proclaimed a ceasefire two years ago, but has so far made no moves to decommission.
The group has been weakened by a number of high profile arrests and flagging support across the Basque region.
Officials have confirmed that two men arrested by armed police in London are suspected Basque terrorists.
Antonio Troitino Arranz and Ignacio Leron Sanchez are described as senior members of ETA by the Spanish interior ministry.
They were arrested at a residential address in Hounslow, west London.
Armed officers joined those from the counter terrorism command when the arrests were made at about 4am.
Police say the operation was not linked to the Olympics.
A 38-year-old woman was also arrested for alleged fraud offences and two other men were held over alleged immigration offences.
The men, aged 39 and 55, were picked up by officers from Scotland Yard's counter terrorism command.
Both are being held under the Extradition Act after being arrested at a residential address in west London.
Scotland Yard says two Spanish nationals have been arrested in London in connection with alleged terrorist offences in Spain.