Five small bombs exploded on highways near the Spanish capital Tuesday following a warning call from the armed Basque group ETA, the Interior Ministry said. No one was injured and there was little damage.

Earlier, a small bomb exploded outside a post office in the northern town of Alsasua, also causing no injuries and little damage. No one claimed responsibility for that blast, but police blamed ETA.

The explosions occurred on a major national holiday commemorating the 27th anniversary of the constitution, which the right has said is what maintains Spanish unity. ETA is seeking an independent Basque state in the north.

ETA has frequently exploded bombs on highways to coincide with national holidays. On Dec. 3, 2004, six small bombs exploded at gas stations around Madrid at the start of the constitution holiday break.

Tuesday's blasts were "another demonstration of senseless violence and only confirm that we have to continue fighting ETA with all the might of the democratic state," Interior Minister Jose Antonio Alonso said.

The explosions caused major traffic delays for millions of Spaniards who had taken to the roads for brief holiday trips.

Police also evacuated an airport in the northern city of Santander after the Basque daily Gara said it received a warning from someone speaking on ETA's behalf that one or more bombs would go off there, the Interior Ministry said.

No bombs were found in a search outside the terminal, and police also were searching inside, Interior Ministry spokesman Agustin Ibanez said.

About 200 people were evacuated and four incoming flights were diverted to other airports, while three outgoing flights were delayed.

ETA has claimed responsibility for more than 800 killings since the late 1960s in its campaign for a Basque state, but it has not killed anyone since May 2003.

In recent months, it has targeted airports and businesses with small explosives.

Spanish news reports said the group insisted in its latest internal newsletter that the Spanish and French governments must make the first moves to halt the violence.

"Spain and France must recognize the Basque region's right to self determination," reports quoted the communique as saying.

The Socialist government has offered to talk with ETA if it renounces violence.