PALMA DE MALLORCA - Spain's security forces were on maximum alert Friday for the 50th anniversary of the armed Basque group ETA, blamed for bombings that killed two police officers and injured scores of people this week.

ETA was founded on July 31, 1959, and has killed more than 825 people since beginning its violent campaign for an independent Basque state in 1968.

Authorities blame ETA for two attacks this week - an explosion that killed two officers near a police barracks on Mallorca island on Thursday and a car bomb that injured more than 60 people in the northern city of Burgos on Wednesday.

If confirmed as ETA attacks, the blasts would conflict with government assertions that the group is seriously weakened after major police crackdowns in Spain and France in recent years.

Their timing, two days before the milestone anniversary, may be part of an ETA effort to demonstrate it is in no danger of breaking up.