European ministers have warned that dormant Islamic terrorist cells could strike at any time.
That warning heightened worldwide alerts against al-Qaeda after suicide bombings in Saudi Arabia and Morocco.
"There are dormant Islamic terrorism cells which could wake up and commit attacks," Italian Interior Minister Giuseppe Pisanu told reporters after meeting counterparts from Madrid, Paris and London in Spain yesterday.
"No one can say they are excluded or safe from an attempted attack by radical Islamic terrorism and that is exactly why we have to reinforce all our security measures," Spanish Interior Minister Angel Acebes said.
Earlier, a Spanish Interior Ministry source said security had been stepped up in the Strait of Gibraltar separating Spain from Morocco, where suicide bombings on Friday killed 41 and injured scores.
Saudi Arabia and Morocco announced the detention of suspected Islamic militants, and the Saudis said yesterday they were looking seriously at al-Qaeda links to last week's bombings in the capital Riyadh.
Suicide attackers killed Westerners, including Americans, in Riyadh, and several Europeans in Morocco's Casablanca. Both Arab kingdoms have historically close ties with Washington.
US officials said Osama bin Laden and some fellow al-Qaeda leaders were believed to be hiding in the border region between Pakistan and Afghanistan, while others were thought to be in Iran. Tehran denies sheltering al-Qaeda members.
Morocco and Saudi Arabia were among Muslim states listed as "most eligible for liberation" in a tape purportedly made by the al-Qaeda leader and broadcast in February.