BERLIN -- Authorities say a van crashed into a crowd Saturday outside a popular bar in the German city of Muenster, killing two people and injuring 20 others. The driver of the vehicle shot and killed himself after the crash, local police said. Six of the injured are listed in critical condition.

It's not yet clear who the suspect is or what the motive is. Police said they are examining reports that other suspects may have fled the crash scene.

The incident is being treated as terrorism, but the suspect's identification has not yet been transferred to the U.S., a U.S. intelligence source told CBS News.

Herbert Reul, the interior minister of North Rhine-Westphalia state, said the driver was a German citizen. Reul stressed the investigation is at an early stage but said "at the moment, nothing speaks for there being any Islamist background."

"We are investigating in all directions," he explained, according to the Associated Press. Reul said two people were killed in the crash, lowering the previous figure provided by police.

Germany's Sueddeutsche Zeitung newspaper reports that the suspect's apartment was being searched for possible explosives.

On Twitter, local police warned residents to "avoid the area near the Kiepenkerl pub" in the city's historic downtown area where a large-scale police operation was underway.

Police said a suspicious object was found in the van and they're still examining it to see if it is dangerous. They told German news agency dpa that the object was the reason why a large area around the scene was sealed off after the crash.

Residents said they were enjoying the first warm afternoon in the area that features many shops and cafés, CBS News correspondent Roxana Saberi said on CBSN. People were outside enjoying themselves, many of them college students, enjoying the weather.

In the hours following the crash, residents lined up outside Muenster University Hospital where people offered to donate blood to victims. The hospital was forced to suspend its call for donors because so many people came forward. "We thank you for your overwhelming support," the hospital tweeted Saturday.

Jan Schoessler, one of those waiting in line, told the AP that dozens of people were waiting shortly after the doors opened at 7 p.m. local time.

Daniel Kollenberg, a witness, said there was a heavy police presence at the scene, with dozens of police vehicles and several police helicopters. "It's quite chaotic because it's pretty calm here," Kollenberg told BBC News. "People are kind of scared. They didn't believe it would happen in Muenster because it is really secure here and so, yes, I am shocked."

A spokeswoman for German Chancellor Angela Merkel said "our thoughts are with the victims and their families" who were killed and injured when a vehicle crashed into a crowd in the western German city of Muenster. 

Ulrike Demmer, a German government spokesperson, tweeted that the crash was "terrible news." 

Germany has experienced a number of terror attacks in recent years, including through the use of vehicles. In December 2016, a truck plowed into a crowd at Christmas market in Berlin, killing 12 people. 

Since the 2016 attack, German authorities have set up road blockades around various areas where people congregate, but it's hard to put barricades around every area where there are crowds, Saberi reports.

German President Frank-Walter Steinmeier said his thoughts are with the victims and relatives of the crash in Muenster.

"We have to assume this was a serious act of violence," he said. "My deep sympathy goes to all those who have lost a loved one."