(AP) French, German and Belgian police arrested more than two dozen suspects in anti-terrorism raids Friday, as European authorities rushed to thwart more attacks by people with links to Mideast Islamic extremists.

Rob Wainwright, head of the police agency Europol, told The Associated Press that foiling terror attacks has become "extremely difficult" because Europe's 2,500-5,000 radicalized Muslim extremists have little command structures and are increasingly sophisticated.

Highlighting those fears, a bomb scare forced Paris to evacuate its busy Gare de l'Est train station during Friday morning rush hour. No bomb was found. A man also briefly took two hostages at a post office northwest of Paris, but police said the hostage-taker had mental issues and no links to terror.

Visiting the tense French capital, U.S. Secretary of State John Kerry met President Francois Hollande and toured the sites of last week's terror attacks: the satirical newspaper Charlie Hebdo and a kosher supermarket. Twenty people, including the three gunmen, were killed.

One of those Paris attackers had proclaimed allegiance to the Islamic State group, and French and German authorities arrested at least 14 other people Friday suspected of links to IS.

Thirteen more people were detained in Belgium and two were arrested in France in a separate anti-terror sweep following a firefight Thursday in the eastern Belgian city of Verviers. Two suspected terrorists were killed and a third wounded in that raid on a suspected terrorist hideout. Federal magistrate Eric Van der Sypt said Friday the suspects were within hours of implementing a plan to kill police, either on the street or in their offices.

In more than a dozen raids Friday, Belgian forces found four military-style weapons including Kalashnikov assault rifles, Van der Sypt said. They also found several police uniforms, which could have allowed the suspects to pass themselves off as police officers.

Belgian officials were reasonably confident they dismantled the core of an important terrorist cell but Van der Sypt said more suspects could be at large.

"I cannot confirm that we arrested everyone in this group," he told reporters.

Authorities did not give many details about those detained or killed in Belgium but said most were citizens and some had returned from Syria. They stressed that the targets of their crackdown had no known connections to last week's attacks in France.

French Prime Minister Manuel Valls said Friday that while there was no apparent operational connection between the two terror groups, "the link that exists is the will to attack our values."

Belgium has seen a large number of residents join extremists in Syria.

"It's the worst affected country in Europe relative to population size," said Peter Neumann of the London-based International Center for the Study of Radicalization. He estimates 450 people have left Belgium to fight with Islamic radicals in Syria and that 150 of them have returned home.

Around the world, protesters rallied against Charlie Hebdo in several countries Friday. The satirical newspaper had 12 employees slain for lampooning the Muslim Prophet Muhammad but it defiantly put a new Muhammad cartoon on the cover of its first post-attacks issue this week. The issue sold out its 3 million copies - more than 50 times its usual press run.

In Karachi, Pakistani students clashed with police and an Agence France-Presse photographer was shot and wounded in the melee. In Algeria, demonstrators protesting Charlie Hebdo thronged the streets of Algiers, the capital.

Many Muslims view the caricatures of Muhammad as a profound insult to Islam.

Across Europe, anxiety has grown as the hunt continues for anyone who helped the three Paris gunmen - French police earlier told AP there could be up to six possible accomplices.

The Paris prosecutor's office said at least 12 people were arrested in anti-terrorism raids in the area, targeting people linked to kosher market gunman Amedy Coulibaly, who claimed ties to the Islamic State group. France has put the country on high alert and deployed 122,000 police and troops to protect citizens, especially at Jewish schools and transport hubs.

The Belgian government on Friday decided to start using its army for some public security tasks, part of a 12-point anti-terror plan lawmakers agreed upon in less than 24 hours since the deadly clash Thursday night. The government will also expand legislation to make traveling abroad with a terror goal a crime and allowing authorities to withdraw ID from people suspected of traveling to such areas.

In Berlin, police arrested two men Friday morning on suspicion of recruiting fighters for the Islamic State group in Syria. Prosecutors said 250 police officers raided 11 residences at dawn, part of a months-old investigation into Turkish extremists.

Kerry's visit to France came after the Obama administration apologized for not sending a higher-level delegation to Sunday's massive rally in Paris, which drew more than 1 million people to denounce terrorism. Hollande thanked Kerry for offering support.

"You've been victims yourselves of an exceptional terrorist attack on Sept. 11. You know what it means for a country," Hollande said. "Together, we must find appropriate responses."

In a separate speech to diplomats, Hollande said France is "waging war" against terrorism and will not back down from its international military operations against Islamic extremists in Iraq and North Africa. France's Parliament voted this week to extend airstrikes against Islamic State extremists in Iraq.

Belgian authorities are separately looking for possible links between a man they arrested in the southern city of Charleroi for illegal trade in weapons and Coulibaly.

Several other countries are also involved in the hunt for possible accomplices to Coulibaly and the gunmen who attacked the newspaper, brothers Cherif and Said Kouachi.

A senior Iraqi intelligence official told the AP on Friday that Iraqi intelligence officers warned their French counterparts two months ago that a group linked to Khorasan in Syria was plotting an attack in Paris. The official spoke anonymously because he was not authorized to brief media.

Iraq's prime minister also warned in September of possible attacks in New York and Paris.