MADRID (Reuters) - The Basque separatist guerrilla group ETA could extend its ceasefire in Spain after the release from jail of 22 former leaders of its political wing early on Wednesday morning, Basque sources said. The Basque nationalist sources said they expected ETA, which announced a ceasefire last September, to make a statement soon in which it would announce "either an extension of the current truce or even a definitive ceasefire". Spain‘s highest court on Tuesday overturned prison sentences against the former leaders of radical separatist party Herri Batasuna (HB) for collaborating with ETA over an election video showing armed guerrillas. The Constitutional Court was ruling on seven-year terms meted out in 1997 to the entire directorate of the party. One of them was released last year on health grounds, and the other 22 left prison in the early hours of Wednesday morning after 20 months behind bars. ETA, which declared a ceasefire last September in its three-decade-long fight for independence in the Basque region, has made freedom for Herri Batasuna‘s former leaders a key demand in talks with the government. Madrid has in turn repeatedly called for ETA to declare its ceasefire "definitive" and renounce violence for good. Prime Minister Jose Maria Aznar, speaking on state radio during a visit to the Middle East, said he respected the court‘s decision to overturn the sentences. After days of deliberations, the court‘s 12 members ruled eight to four on Tuesday night that an automatic minimum six-year sentence set down in Spain‘s penal code for collaboration with armed groups was unconstitutional. The judges did not study other elements of an appeal by the jailed activists, who protested their innocence. In December 1997, after a wave of nationwide protests against murders of politicians by ETA, Spain‘s Supreme Court found the 23 leaders guilty of collaborating with ETA by planning to use a video showing armed guerrillas in an election broadcast. Authorities seized the video before it was aired. Spain‘s centre-right government at the time hailed the sentencing as a victory against "accomplices to terrorism". But even moderate Basques termed it politically motivated, and the jailing sparked a violent backlash by ETA and its supporters. Herri Batasuna spokesman Joseba Permach said Tuesday‘s ruling showed the convictions were politically motivated. But more than a year has now passed without an ETA killing, and opinion polls show Spaniards increasingly optimistic about the prospects for a lasting peace. The 23 former HB leaders have been replaced by a more moderate directorate. Last year, HB drew mainstream Basque nationalists into a broadly based political partnership that helped persuade ETA to declare its open-ended truce and saw its support grow in recent local elections. One of those released on Wednesday, Karmelo Landa, said the ruling was an important step for the Basque region, which includes parts of northern Spain and southern France. All mainstream parties said they respected the court‘s decision, and the only voice of criticism came from the Association for Victims of Terrorism, which groups families of some of the 800 people killed by ETA.