German police said Saturday they found a pig's head bearing an "insulting inscription" outside Chancellor Angela Merkel's constituency office in the country's northeast.

A police patrol discovered the animal's head outside the office in the Baltic Sea town of Stralsund in the early hours of Saturday.

A spokesman for regional police refused to be drawn on the nature of the insults, saying only that they were directed at Merkel, who was first elected to parliament in Stralsund 26 years ago.

Merkel's popularity has waned due to her liberal migrant policy. More than a million migrants arrived in Germany last year, many of them fleeing war and poverty in the Middle East and Africa, and concerns about how Europe's largest economy will be able to integrate them are now rife.

The anti-immigration Alternative for Germany (AfD) has been buoyed by concerns over the integration of the more than one million asylum-seekers that arrived in Germany in 2015, becoming the country's third-biggest party.

Merkel's migrant policies have also been contested by some members of her own Christian Democratic Union (CDU) as well as its Bavarian sister party, the Christian Social Union (CSU).

An INSA poll published on Wednesday showed that almost half of Germans did not want her to stay in office for a fourth term after an election next year.