BERLIN (AP) — The Latest on investigation of truck rampage in Berlin Christmas market (all times local):

11:20 a.m.

Polish Prime Minister Beata Szydlo says it is "with pain and sadness we received the information that the first victim of this heinous act of violence was a Polish citizen."

Szydlo told reporters that Monday's attack on a Christmas market in Berlin is a reminder that "Europe must become unified in the fight against terrorism and Europe must take effective action to protect its citizens."

11:10 a.m.

German Chancellor Angela Merkel says she is "shocked, shaken and deeply saddened" by the attack on a Berlin Christmas market that killed at least 12 people Monday.

Merkel told reporters on Tuesday that it would be "particularly sickening" if it turns out the attacker was an asylum-seeker who sought refuge in Germany.

German media have reported that a suspect arrested after the attack was a Pakistani citizen who came to Germany in late 2015 or early 2016.

11:05 a.m.

German Chancellor Angela Merkel has spoken with U.S. President Barack Obama, who expressed his condolences in the wake of the fatal attack on a Christmas market in Berlin.

At least a dozen people were killed when a truck rammed into the busy market in the German capital in what police described as a suspected "terror attack."

Merkel's office says the two leaders spoke by phone early Tuesday, and Obama assured the chancellor of America's full support in investigating the attack.

11:00 a.m.

London's Metropolitan Police say they are reviewing security plans for public events over the holidays after Monday's attacks in Germany and Turkey.

Police said Tuesday they are considering "a range of threats, including the use of large vehicles."

Police say it is routine to review security plans after attacks overseas.

10:55 a.m.

Berlin police are stepping up armed patrols in response to the fatal attack on a Christmas market Monday.

Police said Tuesday on Twitter that the measure is being taken "as a precaution."

At least a dozen people were killed when a truck rammed into a busy Christmas market in the German capital in what police described as a suspected "terror attack."

10:45 a.m.

Berlin's top security official is calling for Christmas markets in the city to remain shut on Tuesday after Monday's attack that killed at least 12.

Germany's Interior Ministry says Berlin's state interior minister, Andreas Geisel, told federal and regional counterparts that operators of Christmas markets in the capital were asked to close out of respect for the victims and their relatives.

The ministry says the officials agreed that Christmas markets and other major events across Germany should go ahead and that decisions on tightening security measures should be made locally.

The federal interior minister, Thomas de Maiziere, said: "Whatever we find out going forward about the exact background motive of the perpetrators, we must not and will not allow our free life to be taken away."

9:40 a.m.

Police in the English city of Manchester say they are increasing patrols of many popular Christmas markets following the attack in Berlin.

Police said Tuesday they had added extra protection at the 10 market sites, which are often thronged with shoppers in the days before Christmas.

Assistant chief Debbie Ford says the increase is in line with Britain's "national response." The country's terror threat has long been judged to be severe, meaning an attack is highly likely.

She says there is no intelligence suggesting an attack in greater Manchester is imminent.

9:25 a.m.

German police have searched a large shelter for asylum-seekers in Berlin in response to the fatal attack on Christmas market Monday.

The dpa news agency reported Tuesday that up to 250 officers took part in the operation at the now-defunct Tempelhof airport overnight.

It quoted a spokesman for Berlin's office for refugee affairs, Sascha Langenbach, saying four men in the late 20s were questioned by police but nobody was arrested.

Several German media, citing unnamed security sources, reported that the suspect in the attack was a Pakistani man who entered Germany late 2015 or early this year.

Police declined to comment on the reports, referring questions to federal prosecutors who didn't immediately respond to calls Tuesday.

8:10 a.m.

Germany's top security official is ordering flags at federal buildings to be flown at half-staff in the wake of Monday's truck attack in Berlin.

Interior Minister Thomas de Maiziere said in a statement Tuesday that the decision was taken as a mark of sympathy following the attack.

Authorities say at least 12 people were killed and almost 50 injured when a heavily laden truck slammed into a Christmas market in the west of the German capital.

Associated Press writers Frank Jordan in Berlin and Greg Katz in London contributed.