Basque separatist group Eta is weaker than ever despite the bombings its suspected role in a string of new bombings, an analyst has told the BBC.
Small bombs went off in Madrid and seven other Spanish cities
Paddy Woodworth, an Irish writer and Basque expert, said public support for Eta had collapsed in the Basque country and arrests had dented its numbers.
He said the bombings on Monday and Friday could reflect a power struggle in Eta between militants and those seeking peace.
The Basque newspaper Gara said it had received calls from people claiming to be from Eta, warning of the bombs.
Mr Woodworth told the BBC World Service's Europe Today programme: "What we are probably seeing is some kind of internal tug of war between a very militant faction and a faction that wants to call a ceasefire.
"The anti-ceasefire faction is using these bombs both as an internal gesture to their own members and also as a gesture to the government of Madrid, saying: We haven't gone away, we are still here.'"
He said Eta's military infrastructure had been left "very weak" after a crackdown by the authorities during the autumn.
French and Spanish police have detained more than 100 Eta suspects on both sides of the border so far this year and seized large quantities of arms and explosives.
Mr Woodworth said the attacks were designed to show the government that Eta could still pose a serious threat.
"These bombs are very highly co-ordinated. They are saying: 'We still have an infrastructure in place which could cause enormous damage.'"
He added that the latest attacks would be embarrassing for Basque separatist party Batasuna, viewed by the Spanish authorities as Eta's political wing.
The bombs would make it "even more difficult" for Batasuna to advance the peaceful dialogue proposed by leader Arnaldo Otegi last month, he said.
"There's an old saying in Eta, going back 30 years, that whenever there's a debate in Eta between the pistol and politics, the pistol always wins," Mr Woodworth said.
"It means the people who are arguing for a purely political solution will either leave and form a political party or become completely marginalised."
Mr Woodworth said Spain's Prime Minister, Jose Luis Rodriguez Zapatero, was very sensitive to accusations of being "soft on terrorism" after withdrawing Spain's troops from Iraq.
He said Mr Zapatero would consequently be sure to continue the firm line pursued against Eta by his predecessor, Jose Maria Aznar.