A German politician from Angela Merkel’s political party has been found dead in circumstances local media are describing as “mysterious”.

Walter Lübcke, who led the district government in Kassel, reportedly died of a gunshot wound to the head in his own garden. Police say no weapon was found at the scene.

The police in the state of Hesse, of which Kassel is a constituent district, are understood to be treating the 65-year-old’s death a murder investigation.

In a statement the district council said it was “bewildered and shocked at the death of the popular and extremely approachable” leader, while other local politicians also paid their respects to a man one ally described as “bridge-builder”.

Last month the Christian Democrat (CDU) politician celebrated his tenth anniversary as regional president. German media says the politician was expected to retire in March, but that he had extended his tenure at the request of his colleagues.

“We are deeply shocked by the sudden death of our friend Walter Lübcke,” said the CDU state chairman, prime minister Volker Bouffier, and the Hessian CDU parliamentary group leader Michael Bodenberg in a statement.