MADRID, July 15, 2008 (AFP) - A plan for a referendum on self-determination in Spain's northern Basque Country became law in the region Tuesday, setting the stage for a confrontation with the government in Madrid which has termed the poll illegal.

The plan envisages the recognition by Madrid of the right of self-determination for the Basque people, a demand of the armed separatist group ETA, blamed for the deaths of 823 people in its 40-year campaign for an independent Basque homeland.

The measure, which the Basque parliament approved by a narrow majority on June 27, became law Tuesday when it was published in the official journal.

The Socialist government in Madrid has said the referendum as illegal, and vowed to take the issue before the Constitutional Court on the same day the law is promulgated.

'It is the government's duty to serve the constitution,' Deputy Prime Minister Maria Teresa Fernandez de la Vega said of the plan last month. 'There is no place for challenges to the norms of democracy.'

The referendum is the first part of a proposed 'road map' for new political relations between the northern region and Madrid.

The head of the Basque government, Juan Jose Ibarretxe, first announced the plan after ETA formally called off a 15-month-old ceasefire in June 2007.

In May, he revealed the questions that would be put to voters on October 25.

1: 'Do you support a process aimed at negotiating an end to violence if ETA first demonstrates, unequivocally, its will to definitively end violence?'

2: 'Do you agree that Basque political parties should begin a process of negotiation to reach an agreement on a democratic accord on the Basque people's exercise of the right of self-determination and that this accord be submitted to a (regional) referendum before the end of 2010?'

Spain's Socialist Prime Minister Jose Luis Rodriguez Zapatero said he would be open to granting more autonomy to the affluent region, which already enjoys a high level of self-government, as long as this respected the constitution and was the result of a broad agreement on the part of Basque political parties.