A railroad worker found a bomb with seven detonators buried in the bed of a commuter line between France and Switzerland on Wednesday, touching off a massive inspection of the French railroad network.

It was the second bomb found in just over a month on a railroad track in France. Bomb disposal experts neutralized the device, which was half-buried under a track in the village of Montieramey, on a train line heading from Paris to Basel, Switzerland (search), about 105 miles southeast of Paris (search).

There was no immediate claim of responsibility for the bomb, which was discovered shortly after noon. The train line extends from Paris to Basel, Switzerland.

France has been on a higher terror alert since the March 11 train bombings in Madrid, Spain, that killed 190 people. Those bombings prompted the tightening of security on train lines around the world, including in France, Greece and Poland.

In the United States, Amtrak has increased police patrols and intensified electronic surveillance of bridges and tunnels. Major cities, including New York and Washington, have also boosted security on their subway systems.

Suspicion for the Spain attacks has focused on an alleged Morocco-based terrorist cell believed linked to Usama bin Laden's (search) Al Qaeda network and on Al Qaeda (search) itself.

Gen. Patrick Hughes, the top intelligence official at the U.S. Department of Homeland Security, said that if the bomb found Wednesday in France "was an Al Qaeda-sponsored effort, one should expect to find other devices or to be struck in more than one way."

France's Interior Ministry said the bomb did not resemble one found in February on a railroad track near Limoges in central France, located with clues from a previously unknown group calling itself AZF (search). The group claimed to have planted nine bombs along the country's rail network and has threatened to explode them unless it is paid millions of dollars.

French Interior Minister Nicolas Sarkozy said there were "a certain number of elements" that lead officials to believe the two cases may not be the same. A ministry official said it was not immediately clear whether the device found Wednesday was capable of exploding.

Police, terrorism experts and intelligence officials held a crisis meeting at the Interior Ministry. The state-run train authority said it would undertake a massive new inspection, starting with tracks carrying passengers and hazardous freight.

The bomb, which was being examined at a police laboratory, was in a clear plastic box measuring about 8 inches by 8 inches. The box contained nitrate fuel and a flat battery linked to seven detonators and a handmade timing device, the ministry said.

About 10,000 maintenance workers inspected thousands of miles of track after the government publicized the first set of threats early this month.

AZF's threats appeared in at least three letters sent to the offices of Sarkozy and President Jacques Chirac (search) on Dec. 10, Feb. 13 and Feb. 17. The letters, demanding $5.2 million, threatened railway targets.

Information from the group led to the Feb. 21 recovery of a sophisticated explosive device buried in tracks near Limoges in central France.

Tests showed that the Limoges bomb was powerful enough to rupture the track, the government said then. It was made from a mixture of diesel fuel and nitrates and had a sophisticated detonator, judicial officials said.

AZF is not the only previously unknown group issuing threats to France.

Last week, two newspapers received letters addressed to Prime Minister Jean-Pierre Raffarin and signed by the "Servants of Allah the Powerful and Wise." That group also was not previously known to French intelligence officials.

The letters threatened possible terror attacks against France and French interests to punish the country for banning Islamic headscarves in public schools beginning next school year.

French embassies in Muslim countries around the world received the same letters, officials said Tuesday.

Sarkozy has said the letters do not resemble typical messages by Islamic extremist groups.

The device found Wednesday was near the town of Troyes -- where Raffarin made a scheduled campaign stop hours later in advance of Sunday's regional elections. Raffarin -- who traveled by plane as is his habit -- called for calm.