The explosive device found on the high-speed Madrid-Seville railway line dominates the front pages of Spain's newspapers on Saturday.
Several point the finger of blame at Islamist militants.
Some papers see political lessons for the incoming government of prime minister-elect Rodriguez Zapatero.
El Pais says the fact the same kind of explosives and a similar detonator was found in Friday's bomb to those used in the Madrid attacks on 11th March "suggests that in both cases it is the same terrorist organisation, supposedly the Moroccan Islamic Combatant Group".
The paper says that if the same group that carried out the Madrid bombings was responsible for planting the device on Friday, it poses a "very serious security problem".
"It indicates... we are not talking about a passing terrorism... but a stable presence prepared for any barbarity," it says in an editorial.
Under the headline "Living under the threat", La Razon expresses shock at the possible consequences if the bomb had not been found in time.
"Our enemies know us well and know how to do us most harm," the paper writes.
"This threat exists, it is now among us and we must prepare ourselves for a long battle which can only have one ending: that of the victory of freedom, democracy and the rule of law in the face of the dark forces of freedom-destroying Islamic fundamentalism."
ABC has some advice for the incoming administration of prime minister-elect Jose Luis Rodriguez Zapatero.
"To blackmail his next government is to blackmail all Spain and all the groups concerned with the national interest. Now, more than ever, this demands dignity, firmness and determination," it says.
"It is not possible to bargain with international terrorism, because neither must a state offer to do so, nor is it what the terrorists are looking for. Rather they are looking for a total backdown. As a result, from now on, Rodriguez Zapatero must take care with every word and move."
"We are not an accidental victim of al-Qaeda, but another front in its terrorist war against the free world," the paper believes.
El Mundo suggests that, but for the effective action of security officials, the 'Friday of Sorrows', as the Friday before Good Friday is known, could have become literally true and "we would be lamenting the savage murder of another few hundred people".
"Together with the letter sent to our embassy in Cairo, in which a terrorist group from Egypt threatened attacks against Spanish interests if Spain does not withdraw its troops from Iraq and Afghanistan within four weeks, this allows us to arrive at the alarming conclusion that Spain is in the firing line of Islamic terrorism," the paper writes.
It warns that if Mr Zapatero were to shorten his timescale on withdrawing Spanish troops from Iraq if the UN does not play a bigger role there, this would be the "same as giving in to terror".
The paper argues that the bomb find proves wrong those who accuse Mr Rodriguez Zapatero of appeasing terrorists with his withdrawal pledge.
"Another bomb does not give the impression of appeased individuals," it says.
BBC Monitoring, based in Caversham in southern England, selects and translates information from radio, television, press, news agencies and the Internet from 150 countries in more than 70 languages.