German authorities are offering a reward of up to 100,000 euros ($105,000) for information leading to the arrest of a Tunisian man suspected of involvement in the Berlin Christmas-market attack, identifying him as 24-year-old Anis Amri.
In a statement issued on December 21, the Federal Prosecutor's Office warned that the suspect could be "dangerous and armed," and urged members of the public to notify police if they see him.
The statement said a search for Amri was under way, with support from police forces in all of Germany's 16 federal states.
Twelve people were killed and 48 wounded in the truck attack on a Christmas market late on December 19.
German media have reported that the Tunisian suspect has used various identities since coming to Germany in 2015.
Earlier, Ralf Jaeger, the interior minister in the German state of North Rhine-Westphalia where the suspect had lived, said the suspect's asylum request had been rejected and that he was due to be flown back to Tunisia in August but didn't have the necessary papers to be returned.
He added that the suspect was known by Germany's counterterrorism center and his case discussed by intelligence officials as recently as last month.
Jaeger said that legal proceedings against the man had been opened on the suspicion that he was planning a "serious crime."
German authorities are focusing their search in western Germany, where the suspect was registered in a refugee center near the Dutch border.
French President Francois Hollande said on December 21 that his country's intelligence services were in "constant contact" with German officials.
A website linked to Islamic State (IS) extremist group has claimed responsibility for the December 19 attack.
In a December 20 statement, the Amaq website said, "The executor of the operation...in Berlin is a soldier of the Islamic State and he executed the operation in response to calls to target nationals of the coalition countries."
A similar attack with a truck -- driven by a Tunisian man-- in the French resort city of Nice in July killed 86 people.
German authorities had initially arrested a Pakistani asylum seeker who had been the sole suspect in the case but prosecutors said they lacked evidence against the 23-year-old Pakistani man and released him.
German President Joachim Gauck visited some of the nearly 50 people who were injured in the incident. Officials said 14 people are considered to be in serious condition.
"My visit is a symbol of millions of people across our country taking an interest in the fate of the victims, and those who are fighting for their lives, and others who have a good chance to fully recover," Gauck said.
German Chancellor Angela Merkel has said the truck rampage, in which the vehicle plowed 80 meters through the crowd, "would be especially hard for us all to bear if it were confirmed that [the] person who committed this act was someone who sought protection and asylum" in Germany.
Merkel is under fire over her decision in 2015 to admit almost 900,000 migrants -- most from Syria, Iraq, and Afghanistan -- into Germany on humanitarian grounds as they backed up on southern EU borders.
The deadly attack at the Christmas market in the center of the German capital has shocked average Germans and angered Merkel's political opponents.
Police say the truck used in the attack was hijacked by the suspect from a Polish driver, who was found injured in the passenger's seat of the truck.
Police say he was alive at the time the truck drove into the shoppers at the Christmas market but medics were unable to save him.
The White House condemned "what appears to have been a terrorist attack" and said the "horrific incident" appeared to "target our way of life."
The U.S. State Department issued a European travel alert in November warning Americans of a "heightened risk of terrorist attacks throughout Europe, particularly during the holiday season," and urging "caution at holiday festivals, events, and outdoor markets."
Series Of Attacks
The attack in Berlin is the latest in a series of similar incidents in Germany since the summer.
In July, a 17-year-old claiming to be an Afghan asylum seeker attacked passengers on a Bavarian commuter train with an ax and a knife. A week later, a 27-year-old Syrian asylum seeker blew himself up outside a music venue in the Bavarian town of Ansbach, injuring more than a dozen people.
A 12-year-old boy with dual German-Iraqi citizenship also allegedly attempted to explode a nail bomb at a Christmas market in the western German city of Ludwigshafen a few weeks ago.
Christmas markets have a long history in Germany stretching back to the Middle Ages and have grown dramatically to become popular places to socialize -- to drink mulled wine and to eat snacks in the weeks running up to Christmas.
Security has been increased at Christmas markets all over Germany, where nearly every town and city has such a market during the holiday season.
With reporting by Reuters, AP, AFP, N-TV, Der Spiegel, and dpa