FRANKFURT/SAN FRANCISCO (Reuters) - A Tesla Motors Inc car operating under Autopilot collided with a bus in northern Germany, but the electric car maker said a collision was unavoidable because the bus swerved into the vehicle's lane.

The incident occurred on Wednesday in the town of Ratzeburg, German police said.

The car's driver told Tesla following the crash that he was using Autopilot when the incident occurred but that it was unrelated to the accident, a Tesla spokeswoman said on Thursday.

"We have spoken to our customer, who confirmed that Autopilot was functioning properly and that his use of Autopilot was unrelated to the accident," Tesla said in a statement.

Reuters could not confirm independently what the car driver told Tesla and the circumstances that caused the bus to swerve.

Tesla's Autopilot, introduced last October, helps drivers steer and stay in lanes and is intended to assist, but not replace, drivers. It has been the focus of intense scrutiny since it was revealed in July that a Tesla Model S driver was killed while using the technology in a May 7 collision with a truck in Florida.

Since then, there have been various reports of accidents involving Teslas whose drivers were using Autopilot, including a fatality in China, but it is not clear what role, if any, the driving assistance system played. There have also been reports of serious accidents prevented because of Autopilot.

Police in Ratzeburg said in a statement on Thursday that the 50-year-old driver from Brandenburg drove into the back of a Danish tour bus as it was returning to the inside lane after overtaking. Police said they planned to investigate "why (Autopilot) did not work."

The Tesla driver was slightly injured but none of the 29 bus passengers were hurt, the statement added. Authorities were not immediately reachable by telephone after hours on Thursday.

Tesla denied that Autopilot was at fault, saying the bus swerved into the car's lane and side-swiped the Tesla, making a collision "unavoidable," the spokeswoman said.

"We can only do so much to prevent an accident," she said, adding that Tesla was in contact with German police.

Reuters was not immediately able to reach German police for comment.

The Silicon Valley automaker said this month it was updating the semi-autonomous driving system with new limits on hands-off driving and other improvements.

(Reporting by Georgina Prodhan in Frankfurt and Alexandria Sage in San Francisco; Editing by Emma Thomasson, Matthew Lewis and Lisa Shumaker)