Berlin has slammed Ankara's refusal to allow German lawmakers to visit a NATO base near Syria and warned it could move its troops elsewhere.
The German foreign ministry described as "absolutely unacceptable" Turkey's latest ban on a visit to the Incirlik base in southern Turkey, used by the international coalition fighting Daesh.
Germany has about 250 military personnel stationed there, flying Tornado surveillance missions over Syria and refueling flights for partner nations battling Daesh militants.
Chancellor Angela Merkel said Turkey's position was "unfortunate" and that Germany, while continuing talks to resolve the issue, would also "search for alternatives to Incirlik", including in Jordan.
A defense ministry spokesman said Jordan offered "the best conditions" after Berlin had also looked at Kuwait and Cyprus since Turkey first denied such visits to German MPs for several months last year.
The spokesman cautioned however that any move would involve shifting hundreds of containers of materiel and would take several months.
Turkey rejected the latest lawmakers' visit because of anger over Germany granting political asylum to some of its military officials since last year's failed coup against President Recep Tayyip Erdogan, foreign ministry spokesman Martin Schaefer suggested.
He said Ankara's reason may be "individual decisions of independent German authorities in connection with military members".
Merkel stressed that, since Germany's military missions always require parliamentary mandates, "it is absolutely essential that our lawmakers are able to visit our soldiers".
Hundreds have sought asylum
German media have reported that over 400 Turkish military personnel, diplomats, judges and other officials and their relatives had sought political asylum in Germany.
They fear being caught up in Turkey's crackdown against those Erdogan blames for the coup - supporters of Fethullah Gulen, a reclusive US-based Muslim cleric who has denied the charges against him.
The vast crackdown has heightened tensions between Turkey and Germany, which is home to a three-million-strong ethnic Turkish population, the legacy of a massive "guest worker" program in the 1960s and 1970s.
Both countries have sparred over a range of issues, including civil rights in Turkey, freedom of expression, the military campaign against Turkey's Kurdish minority and a prospective Turkish referendum on reintroducing the death penalty.
Relations were strained further since the arrest of Turkish-German journalist Deniz Yucel on terror-related charges in February, and during the referendum campaign in April to boost Erdogan's powers.
Another row last year, centered on a sensitive historical question, had led Turkey to deny German lawmakers the right to visit Incirlik for several months.
The German parliament had voted in June to recognize the Ottoman Empire's World War I-era massacre of Armenians as a genocide.
After the vote, a furious Erdogan accused German lawmakers of Turkish origin of having "tainted blood".
Armenians say up to 1.5 million people were killed between 1915 and 1917 as the Ottoman Empire was falling apart.
Turkey rejects the claims, arguing that 300,000 to 500,000 Armenians and as many Turks died in civil strife when Armenians rose up against their Ottoman rulers and sided with invading Russian troops.
That row was only resolved after Merkel made clear the Armenia resolution was a political statement and not legally binding, allowing German lawmakers to visit Incirlik in October.