French security forces are mobilizing in their search for what the prime minister called a "probably accomplice" to three days of bloodshed and terror around the capital, as well as to try to ensure the safety of the French people.

Manuel Valls said the search is urgent because "the threat is still present" after the attacks that left 17 people dead -- journalists at the satirical newspaper Charlie Hebdo, hostages at a kosher market and three police officers -- plus the three attackers, who were killed Friday in nearly simultaneous raids by security forces.

Meanwhile, France's defense minister said Monday the country is mobilizing 10,000 security forces to protect the population. Jean-Yves Le Drian said the deployment will begin Tuesday, and will focus on the most sensitive locations.

The widow of one of the attackers crossed into Syria on Thursday, the day after the Charlie Hebdo massacre, and the same day her husband shot a policewoman to death on the outskirts of Paris, according to Turkey's foreign minister.

Mevlut Cavusoglu told the state-run Anadolu Agency on Monday that Hayat Boumedienne arrived in Turkey from Madrid on Jan. 2, ahead of the attacks and stayed at a hotel in Istanbul before crossing into Syria on Thursday. Security footage released Monday shows Boumedienne inside an Instanbul airport last week.

Meanwhile, video emerged on Sunday of her husband, Amedy Coulibaly, explaining how the attacks would unfold and police want to find the person who shot and posted the video, which was edited after the attacks were over.

Police also discovered the hideout where they believe Coulibaly – who is suspected of killing a police officer and then four other people inside a Kosher supermarket – prepared for his attacks, sources told ABC News.

French authorities told the network that Coulibaly rented an apartment in a Paris suburb a week prior to the attack. Police reportedly found weapons and ISIS flags when they raided the apartment on Sunday.

Valls told BFM television on Monday that France is at war against "terrorism, against jihadism, against radical Islam."

Survivors say the Charlie Hebdo attackers, brothers from Paris, claimed they were from Al Qaeda in Yemen, the group the U.S. considers the most dangerous offshoot of that network. In the video, Coulibaly pledges allegiance to the Islamic State group.

But ties among the men date back to at least 2005.