Second Paris Bomb in 3 Weeks Injures 17 : Terrorism: Many of those hurt in blast near Arc de Triomphe are tourists.

A butane-gas bomb loaded with nails exploded Thursday in a trash can near the Arc de Triomphe, injuring 17 people and raising new fears that a deadly subway bombing three weeks ago was just the beginning of a summer terrorist campaign by Muslim militants.

The latest device, which seriously wounded three people, was planted across from the French landmark, near a newspaper kiosk and a subway entrance. The area, near the famed Champs Elysees, usually is crowded with tourists.

Police said Thursday’s device was similar, though less powerful, than a bomb that killed seven people July 25 in an underground train station in central Paris.

Minutes after Thursday’s blast, hundreds of police blocked off the area, and across this capital city, officers began searching men and women leaving subway cars. Some rail lines also were halted briefly as police conducted car-to-car searches.

French radio stations reported that police detained two people in a Mercedes-Benz with Iranian diplomatic license plates; the vehicle reportedly was seen near the bomb site. Iranian government officials denied any involvement in the blast, and no one immediately claimed responsibility for it.

Radio reports suggested that as many as 11 of the injured were foreign tourists, including at least three children.

The blast came after nearly a month of heightened security across Paris. Since the subway blast, police have sealed all trash canisters in subway and regional train stations; stopped and checked identity papers of tens of thousands of foreigners; and sent extra foot and motorized patrols onto the streets.

“We can’t accept this kind of cowardly, criminal and revolting act,” said Interior Minister Jean-Louis Debre, who vowed to send even more police onto the streets in coming days.

Although no one has been arrested in the July subway bombing, the worst terrorist attack here in almost a decade, police have said they suspect Muslim militants angered over French dealings with the government in the North African nation of Algeria.

Radical Muslim groups there want to overthrow the military-backed government and create an Islamic state. France is home to many Algerians, and French police contend that the country has been used as a base of operations for Algerian guerrillas.

Some political analysts suggested that Basque separatists in Spain, angered over the arrests of some of their members in southern France this week, also could have been behind Thursday’s blast.

Within hours of the explosion, tourists again thronged the Champs Elysees cafes and theaters.

Christopher Scott, who had just arrived from Scotland with his wife, Jean, for a five-day vacation in Paris when the bomb went off, said his holiday plans would not be interrupted. “But,” Scott noted, “we’re going to avoid tourist places.”

Sarah White of The Times’ Paris Bureau contributed to this report.