(This May 15 story has been refiled to correct description in second paragraph to .. U.S.-led mission ..not.. NATO’s mission.)

FILE PHOTO: German Defence Minister Ursula von der Leyen chats with soldiers during a visit of the German Armed Forces Bundeswehr at the air base in Incirlik, Turkey, January 21, 2016. REUTERS/Tobias Schwarz/Pool/File Photo

ANKARA/BERLIN (Reuters) - Germany could move troops now based in Turkey to another country if Ankara persists in denying German lawmakers permission to visit them, Chancellor Angela Merkel said on Monday, highlighting renewed strains between the NATO allies.

Some 250 German troops are stationed at Incirlik air force base, contributing to the U.S.-led mission targeting Islamist State militants in neighboring Syria. Turkish foreign ministry sources told Reuters a visit by German parliamentarians would not be appropriate at this time, without elaborating.

Turkey similarly refused access to German parliamentarians late last year, though that visit eventually went ahead.

“We will continue to talk with Turkey, but in parallel we will have to explore other ways of fulfilling our mandate,” Merkel told reporters on Monday.

“That means looking at alternatives to Incirlik, and one alternative among others is Jordan,” she said.

A German military survey team will visit Jordan in coming days to look at potential bases there, government sources said. Jordan is the preferred site, although facilities in Cyprus and Kuwait are also possible, they said.

For historic reasons and to prevent abuse of power, the Bundeswehr army is controlled by the German parliament, not the government, meaning that lawmakers have the right to inspect its activities, including outside the country.

“COMPLETELY UNACCEPTABLE”

A spokesman for the German foreign minister said it was “completely unacceptable” for Turkey to keep members of the parliamentary defense committee from visiting their own soldiers.

Foreign Minister Sigmar Gabriel will raise the issue with colleagues from other NATO governments in Washington on Tuesday, the spokesman added.

German and NATO military officials still hope to avert a wider rift with Turkey given the importance of NATO facilities there, including a powerful radar that supports the Aegis Ashore missile defense site in Romania.

Moving the German troops from Incirlik could also result in a two-month interruption in the surveillance flights they are now conducting from the Turkish base, a government source said.

The German militry has long planned to invest over 60 million euros to expand housing and equipment at Incirlik, but Turkey has not yet approved the plans.

Relations between Ankara and Berlin deteriorated sharply in the run-up to an April 16 referendum in Turkey on expanding President Tayyip Erdogan’s powers.

Citing public safety concerns, Germany banned Turkish politicians from addressing rallies of expatriate Turks, prompting Erdogan to accuse Berlin of “Nazi-like” tactics. A narrow majority of Turks in the referendum backed changing the constitution to grant Erdogan sweeping executive powers.

Germany and other Western allies have voiced concern about what they fear is a drift towards authoritarian rule in Turkey.

Last year Turkey banned German lawmakers from visiting the base for months in response to a resolution in the German parliament declaring the 1915 massacre of Armenians by Ottoman forces a genocide, a term Ankara rejects.