Did their voices betray them? The discovery of an alleged terror plot against Europe owes at least some of its success to "voiceprint" technology that allows law enforcement to electronically match a voice to its owner.

The technique - which some compare to fingerprinting - can be a powerful anti-terror tool, officials increasingly believe. Law enforcement agencies are already considering how a voice database could help thwart future plots.

The suspected plot against European cities in which suspects allegedly spoke of a Mumbai-style shooting spree has triggered travel warnings and refocused attention on al-Qaeda activities on the Pakistan-Afghanistan border, where several suspects' voices were recorded.

The British eavesdropping agency GCHQ deployed voice identification software to help uncover the plot that officials say has targeted Germany, Britain and France.

"Advances in these types of technology have been key in thwarting plots and catching suspects," a British government official said, speaking on condition of anonymity because of the sensitivity of his work.

Despite progress made in quashing the plot, officials still speak of an ongoing threat.

Police in southern France on Tuesday arrested 12 suspects in sweeps against suspected Islamic militant networks.

In one of the cases, nine suspected Islamic militants were detained in southeastern Marseille and its suburbs, and authorities turned up at least one automatic rifle and a pump gun, officials said.

In Tuesday's other roundup, two men were arrested in Marseille and another in southwestern Bordeaux on suspected ties to a Frenchman accused of links to an Afghan recruiting ring.

Officials in Germany were tight-lipped on Tuesday on details of a US missile strike in Pakistan's rugged mountain border area, where Pakistani officials said five German militants were killed.

US officials believe a cell of Germans and Britons was at the heart of the Europe terror plot.

Developers of voice biometric technology say it can be more useful than traditional fingerprint analysis in fighting terror.

"You have potential for there to be a larger database for criminals' voices than their fingerprints. What are the chances that you'll get a foreign terrorist's fingerprint versus a foreign terror suspect's voiceprint?" said Germano di Mambro, who runs Porticus Technology Inc in Wellesley, Massachusetts.

But academics in the field of speech processing have offered caution. In a 2003 paper presented to a conference in Geneva, several experts warned that there was no scientific way of identifying a person's voice with absolute certainty.

Frederic Bimbot, one of the paper's authors, said the term "voiceprinting" was a misnomer because it suggested that the technique was as reliable as fingerprinting.

"This is absolutely not the case," his paper said, noting that, unlike a persons' prints, voices are highly variable - changing according to age, health, and emotional state.