Hundreds of thousands of Spaniards have staged an anti-terrorism rally in Madrid, as the death toll from Thursday's bombings continued to rise.
A seven-month-old baby died Friday, bringing the toll to 199.
Earlier, people across Spain stopped for a moment of silence and, in Washington, President Bush took part in a wreath-laying ceremony at the Spanish ambassador's residence. He said the United States stands firmly with Spain against terrorism.
Earlier, Prime Minister Jose Maria Aznar said investigators will pursue every lead in the hunt for those responsible for the devastating loss of life. He also pledged that Spain will share all information it gathers about the bombings, which killed people from 11 countries.
Little information has come out so far, but one radio station quoted security services Friday as saying an unexploded bomb found near one railroad station had a detonator not like those used in the past terrorist attacks by the Basque separatist movement ETA. Initially, authorities blamed ETA for the attacks, and Friday, ETA again denied any responsibility. Officials are also considering a possible role by the al-Qaida terrorism network. The Abu Hafs al-Masri Brigades, affiliated with al-Qaida has claimed responsibility for the blasts. Al-Qaida earlier had named Spain as a target because of its strong support for the U.S.-led war in Iraq.
Other European countries tightened transportation security as many of their leaders went to Madrid to join the anti-terrorism rally Friday evening.
Italian Prime Minister Silvio Berlusconi, French Prime Minister Jean-Pierre Raffarin and German Foreign Minister Joschka Fischer are among those attending. Elsewhere, millions of Spaniards were expected to take part in parallel ceremonies.
Three days of mourning are in effect, and the final days of campaigning for Spain's national elections have been suspended. But the government says voting will take place Sunday as scheduled.
Thursday's blasts came exactly two-and-one-half years after the terrorist attacks on the United States on September 11, 2001.