Germany's foreign minister has said that Thailand's King Maha Vajiralongkorn should not be conducting politics from the European country, where he spends much of his time. 

Foreign Minister Heiko Maas responded to a question by a Greens member of parliament in the Bundestag on Wednesday at a time that King Vajiralongkorn's monarchy faces unprecedented calls for reform from protesters in Thailand.

"We have made it clear that politics concerning Thailand should not be conducted from German soil," Maas told parliament. "If there are guests in our country that conduct their state business from our soil we would always want to act to counteract that."

Thousands of protesters have been holding demonstrations in Bangkok over recent months calling for reform of the monarchy to curb the king's powers and for the removal of Prime Minister Prayuth Chan-ocha, a former junta leader, and a new constitution and elections.

King Vajiralongkorn, 68, has been on Thailand's throne since 2016, but spends much of his time in Bavaria, where his 15-year-old son is at school.

Thai protesters have complained about the cost of the king's stays in Europe as well as his absence from the kingdom. The protesters seek to reduce the king's powers under the constitution, which specifically allows him to exercise powers when he is outside Thailand without appointing a regent.

Protesters also want to remove his direct control of a royal fortune valued in tens of billions of dollars and some units of the army.  Protesters in Thailand on Thursday said they would rally again next Wednesday and expected a big turnout to pressure the government to meet their demands.