Paris - French police arrested 12 people on Friday suspected of helping militant Islamist gunmen in last week's killings in Paris, where visiting US Secretary of State John Kerry laid wreaths at two main attack sites.The arrests came after Belgian police killed two men and detained 13 suspects on Thursday in raids on an Islamist group prosecutors said was about to attack police there. Two related suspects were arrested in France and German police arrested two people after raiding 12 properties linked to radical Salafists. No link between any of them and the Paris attacks was confirmed.Seventeen victims and the three attackers died in three days of violence in Paris last week that began with an assault on the offices of satirical weekly Charlie Hebdo."A total of 12 persons were detained, most of whom were known to the police for common crimes," French Interior Minister Bernard Cazeneuve said of Friday's police action, relating it to last week's attacks. Judicial sources said the eight men and four women were detained in the greater Paris area.Paris's Gare de l'Est train station was evacuated for about an hour during the morning rush, the SNCF state railway said, without giving further details about the alert.Big hugKerry greeted President Francois Hollande on Friday morning with a hug at the Elysee presidential palace. He said on Thursday his visit was to give a "big hug" to Paris.There were no senior US officials at a commemoration march in Paris on Sunday attended by dozens of world leaders, an absence Washington later conceded was an omission."You have the full and heartfelt condolences of the American people and I know you know that we share the pain and the horror of everything that you went through," Kerry told Hollande."Once again, France, through its commitment to freedom and to the passion of ideas, has made an important statement to the world," he said.Hollande called the shootings France's 9/11, referring to the 11 September, 2001 attacks in New York, and said: "Together we need to find the right responses and this is the purpose of our meeting here today, beyond the friendship."Kerry and his French counterpart Laurent Fabius visited the offices of Charlie Hebdo and the Hyper Cacher kosher grocery, where they laid wreaths in memory of the victims.Later at Paris City Hall, Kerry spoke in English and French about the two countries' friendship and told how his mother, who was born in Paris, fled the city when Nazi Germany occupied it."No nation knows better than France that freedom has a price," he said at a short ceremony where US singer James Taylor performed his song You've Got A Friend. Worst attacksInvestigators are poring over the chain of events that led to three French nationals - two brothers with Algerian roots and a third of West African extraction - perpetrating the worst attacks in the country for decades.In Belgium, a spokesperson for state prosecutors said there was no apparent link between the two men killed during the shoot-out in the eastern city of Verviers and the Paris attacks.Belgian investigators were also examining if a man detained in the city of Charleroi on suspicion of arms trafficking had any links with Amedy Coulibaly, the gunman who killed four Jews at a kosher supermarket in Paris last week.The detained man's lawyer told French media he had merely sold Coulibaly a car.In France, demand for the first post-attack edition of Charlie Hebdo remained high for the third day in a row. One kiosk in central Paris reported a thief broke in overnight and stole all its copies of the weekly.About 200 Pakistani protesters clashed with police outside the French consulate in Karachi after a demonstration against Charlie Hebdo's front-page caricature of Prophet Mohammad.