German Chancellor Angela Merkel said her country should reconsider stationing troops in Turkey, in the latest diplomatic row between the two major NATO allies.

Germany has hundreds of soldiers deployed at the Incirlik air base in southern Turkey as part of Germany’s contributions to the fight against the Islamic State. On a recent trip to the country from members of the German parliament, Turkish officials blocked their state visit over Germany’s decision to allow former Turkish government officials to remain in Germany.

Turkey has insisted the Germans either grant the officials asylum status, or return them to Turkey to “turn its face to the Turkish republic.” Turkey believes these officials to be involved in the failed 2016 coup against the Erdogan government, and they are part of an official “purge” list.

This is not the first time the Turkish government has clashed with German politics. Last year, after German parliament acknowledged the Armenian massacre in 1915 at the hands of the Ottomans as a genocide, Turkey blocked officials from visiting the Incirlik Air Base. Erdogan also infuriated many in Germany when, during the run-up to his own successful presidential referendum in April, he called European leaders ‘Nazi remnants’.

Turkey’s diplomatic belligerence has been cause for concern among many NATO allies, who fear Erdogan’s increasingly centralized presidential powers are a threat to democratic processes in Turkey, as well as a potential vulnerability to the military alliance. The crackdown on political opponents following last summer’s coup is the clearest indication of how political dissidents are treated in the country.

Merkel has indicated that she’s looking into different staging options for the German commitment to combating the Islamic State, which includes reconnaissance and refueling aircraft, as well as soldiers from the Bundeswehr training the Kurds in Iraq.

“We will continue to talk with Turkey, but in parallel we will have to explore other ways of fulfilling our mandate,” Merkel said on Monday. “That means looking at alternatives to Incirlik, and one alternative among others is Jordan.” she said.

Merkel and Erdogan are set to meet in Brussels next week.