PARIS (AP) — Armed soldiers are on guard in Paris' subways, train stations and some of the world's most recognizable monuments to head off terror attacks after France's military launched an operation to push back al-Qaida-linked insurgents in Mali.

Since the operation in Mali began on Friday, the soldiers have reinforced already tight security with a far more visible presence, patrolling in small groups at malls, beneath the Eiffel Tower and outside the Louvre. Security forces stand in twos and threes on subway platforms, patrolling through the pedestrian tunnels and airports in black or camouflage, as part of the national "Vigipirate" program.

Interior Minister Manuel Valls said France is well aware of the dangers of attacks from terrorists angry over the intervention. But he said he believed the long-term threat posed by the advance of militant Islamist fighters in Mali was far greater, because the country could become a potential training ground for terrorists.

Declaring France had "opened the gates of hell" with its assault, the rebels from the Sahel desert region that includes Mali threatened retribution on Monday.

"France is watching individuals who want to go to Afghanistan, Syria and the Sahel. We're watching those who could return here," Valls told the French television network BFM. "We're facing an exterior enemy and an interior enemy."

He said France had already fallen victim to attacks in recent months, referring to a French-born radical Islamist Mohammad Merah who targeted French soldiers and a Jewish school in the south, and a group of men accused of firebombing a kosher grocer in September.

The French government late last year passed a law barring citizens from training for terrorism abroad in response to the deadly attacks in the south by Merah, who received paramilitary training in Pakistan.

Marc Trevidic, a French judge who has investigated terrorism cases, said he was not worried about the threat of attacks in the short term.

"The Malian Islamists currently have other priorities than carrying out a terrorist attack in France," he told Le Parisien newspaper. But long term, he said, the threat is very real, especially given how easy it is to travel between France and Mali. "With this military intervention, we're on the front lines. Suddenly, France is a priority target."

Some 100,000 Malians are residents of France, and there are regular direct flights between Mali's capital, Bamako, and Paris.