* Man shot himself after driving into restaurant, police say
* Too early to speak of attack - police
* German politicians express shock
* Perpetrator was probably German - security source
* Sueddeutsche Zeitung says he had psychological problems (Adds information on perpetrator)
MUENSTER, Germany, April 7 (Reuters) - A man drove a van into a group of people sitting outside a popular restaurant in the old city centre of Muenster in western Germany on Saturday, killing at least two of them before shooting himself dead, police said.
The vehicle ploughed into people sitting at tables outside the Grosser Kiepenkerl restaurant, which is popular with tourists.
"At 15:27 (1327 GMT), a vehicle drove into the outside area of the restaurant ... three people were killed, 20 injured, and six of those seriously injured," police spokesman Andreas Bode said, adding: "The perpetrator killed himself in the vehicle."
It was not immediately clear whether the perpetrator was among the three killed, or whether his death took the number of dead to four. A police spokeswoman said separately that there were at least three people dead.
A security source said the perpetrator was probably German.
The Sueddeutsche Zeitung said the man was a German with psychological problems who had no terrorist background. The Interior Ministry in the state of North Rhine-Westphalia, home to Muenster, would neither confirm nor deny the report.
Bode said the identity of the perpetrator was not yet clear. Investigators were looking at the possibility that other suspects fled the scene, though they had no evidence that this was the case, he added.
"It is far too early to speak of an attack," Bode said. "We have cordoned off the area widely. The crime scene investigators are checking out the crime scene, trying to identify, investigate and secure traces. That is our current task."
The police spokeswoman said: "The danger is over."
The incident came one year to the day after a truck attack in Stockholm that killed five people.
It also evoked memories of a December 2016 truck attack in Berlin that killed 12 people. In that attack, Anis Amri, a failed Tunisian asylum seeker with Islamist links, hijacked a truck, killed the driver and then ploughed into a crowded marketplace, killing 11 more people and injuring dozens of others.
"I am shocked by the news from Muenster," said Andrea Nahles, parliamentary leader of the Social Democrats, junior partner in Chancellor Angela Merkel's ruling coalition.
"My thoughts are with the victims and their relatives," she added. "I hope that our authorities can quickly clarify the background to this incident and wish the local forces much strength for their work."
Government spokeswoman Ulrike Demmer tweeted: "Awful news from Muenster. Our thoughts are with the victims and their relatives."
(Additional reporting by Sabine Siebold Writing by Paul Carrel Editing by Dale Hudson and Hugh Lawson)