Zapatero's Socialists swept to office on Sunday in a shock victory over Prime Minister Jose Maria Aznar's conservatives.
Some analysts said it could be an alarming first case of Islamist fighters influencing, by violence, the outcome of a major Western election.
But Zapatero on Monday called his triumph a first consequence of the Iraq war's unpopularity with Spaniards. "The second will be that the Spanish troops will come back," he told a Spanish radio station.
"Mr Blair and Mr Bush must do some reflection and self-criticism ... you can't organise a war with lies," he said in remarkably frank comments for the next prime minister of Western Europe's youngest democracy and fifth largest economy.
US President George Bush called to congratulate 43-year-old Zapatero. "The two leaders said they both looked forward to working together, particularly on our shared commitment to fighting terrorism," a White House spokesman said. Bush did not ask about a Spanish troop withdrawal.
Zapatero, due to take office within the next month, repeated several times on Monday his campaign pledge to pull out troops unless the United Nations takes charge in Iraq by mid-year - a shift in control that he said was unlikely.
Spain has 1300 soldiers in parts
of south-central Iraq
A US official, who asked not to be named, said Washington could push for a new UN resolution before it hands back sovereignty to Iraqis by the end of June, to encourage allies such as Spain to keep their troops in Iraq.
Spain has 1300 soldiers in parts of south-central Iraq. Critics of the government argued the Madrid bombings were the price Spain paid for backing the Iraq occupation.
"We have been very clear about the risk and the threat that we were all facing with this illegal war in Iraq, and unfortunately Spain has paid the price," Spain's likely next foreign minister Miguel Angel Moratinos told Reuters.
"The sooner we admit that the wrong policy has been made,
the better for the future of the international community."
Most commentators saw Zapatero's shock election victory as driven by anger over Aznar's handling of the suspected al-Qaida attack on Madrid commuter trains that also wounded 1500 people.
"Mr Blair and Mr Bush must do some reflection and self-criticism ... you can't organise a war with lies."
Jose Luis Rodriguez Zapatero
Spain's incoming leader
After Thursday's attacks Aznar's government initially blamed the armed Basque separatist group ETA, which denied involvement.
Sunday would go down in history as "the day when Islamic
fundamentalism was seen as dictating the outcome of a European election", said Wilfried Martens, head of the European People's Party, an umbrella group for European conservative parties.
With almost all votes counted, the Socialists had won 42.6%
of the vote to 37.6% for Aznar's Popular Party. With 164 seats in the lower house of parliament, 12 short of an absolute majority, Zapatero has said he intends to govern through dialogue with other groups. He ruled out the possibility of a coalition with regional parties.
But the PP will remain by far the largest single force in the upper house or Senate, potentially making it difficult for a Socialist government to pass legislation.
The Spanish stock market dropped sharply on Monday amid mounting suspicions of al-Qaida involvement in the bombings and uncertainties over the Socialist party's economic agenda. Some 12 billion euros was wiped from the value of leading companies.
Aznar (R) has supported the
US-led war on Iraq
But in a nod to investors in Spain, Zapatero lined up well-known free-marketeer Miguel Sebastian as his chief economic adviser. Sebastian is tipped to take the economy ministry.
Zapatero said his immediate priorities would be fighting
terrorism and a more "pro-European" foreign policy.
The EU's Irish presidency announced that EU justice and
interior ministers would hold emergency counter-terrorism talks in Brussels on Friday at Germany's request.