Lars Vilks, an artist and free speech activist whose cartoon depiction of the Prophet Muhammad on the body of a dog in 2007 made him the target of numerous assassination attempts, was killed in a car crash in Sweden on Sunday, the police said.
Mr. Vilks, who had been under police protection since 2010, was headed toward his home in southern Sweden when the civilian police vehicle he was traveling in veered across the median and collided head-on with a truck, killing Mr. Vilks, 75, and his two bodyguards, the police said.
The truck driver was taken to a hospital with serious injuries.
“We are looking at the possibility that it was a tire explosion,” Stefan Sinteus, a regional police official, said during a news conference on Monday. “There is nothing at this point to indicate that this was an assassination.”
Mr. Sinteus said the two police officers who were killed in the crash had worked with Mr. Vilks for several years.
The accident occurred on Sunday afternoon along a four-lane highway in Markaryd, an area about 300 miles southwest of Stockholm.
Many Muslims consider depictions of Muhammad to be blasphemous, and cartoons such as the one by Mr. Vilks have prompted widespread backlash over the years. In 2005, a newspaper in Denmark published a caricature of Muhammad wearing a bomb-shaped turban that touched off violent protests by Muslims.
In 2015, Islamic militants stormed the Paris office of the satirical magazine Charlie Hebdo, which had reprinted the cartoon, and killed 12 people.
Mr. Vilks’s black-and-white drawing was published by a regional paper in Sweden in 2007 and was condemned by Muslims in the country, as well as by the Organization of the Islamic Conference, an umbrella organization of 57 Muslim-majority countries.
Mr. Vilks subsequently received death threats, and a group linked to Al Qaeda placed a $100,000 bounty on his head, forcing him to temporarily move to a secret location.
Mr. Vilks was threatened repeatedly after the cartoon was published.
In 2010, he was assaulted while giving a lecture on free speech at Uppsala University in Sweden. That year, two brothers were also jailed after trying to burn down his house. In a separate case, a suicide bomber sent messages to several Swedish news organizations singling out Mr. Vilks before detonating two explosives in central Stockholm, killing himself.
In 2015, a gunman in Copenhagen attacked a cafe where Mr. Vilks was speaking at an event called “Art, Blasphemy and Freedom of Expression,” killing a filmmaker and wounding three police officers. One of the organizers of the event, Helle Merete Brix, said she believed Mr. Vilks had been the intended target, although he was unharmed in the shooting. The police later said they had shot and killed a man they believed was responsible for the attack at the cafe as well as another attack at a synagogue, where one person was killed.
After the attacks, Mr. Vilks traveled with armed bodyguards, according to The Associated Press. “It’s like starting a new life,” he said. “Everything has changed. I have to understand that I cannot go back home. I have to probably find some other place to live.”
Despite offending Muslims and the threats against his life, Mr. Vilks said he had no regrets over the cartoon. “I’m actually not interested in offending the prophet,” Mr. Vilks told The A.P. in 2010. “The point is actually to show that you can. There is nothing so holy you can’t offend it.”