BERLIN (Reuters) - Turkey is blocking the plans of a senior German defence official to visit Incirlik air base in July, a spokesman for the German defence ministry said on Wednesday, in a sign of increasingly tense relations between the two NATO allies.

Germany has about 250 soldiers stationed at the base in southern Turkey, along with six Tornado reconnaissance jets and a refueling plane, all of which are participating in a U.S.-led air campaign against Islamic State militants in Iraq and Syria.

"Turkish officials do not currently approve of the travel plans," a ministry spokesman said, confirming a report published by the website of the German magazine Spiegel.

Ralf Brauksiepe, a deputy to German Defence Minister Ursula von der Leyen, had planned to visit the Incirlik military air base along with some German lawmakers next month, the spokesman said, adding that Berlin still hoped the trip could go ahead.

Turkish officials were not immediately available for comment.

Just last week, a German defence ministry spokesman had said the two countries were finalizing an agreement on construction of new housing and aircraft facilities for German forces at the Incirlik air base, holding the deal up as evidence of the continued strength of German-Turkish military relations.

Ties between Germany and Turkey have been strained over a number of issues, including a resolution adopted by the German parliament that declares the 1915 massacres of Armenians by Ottoman Turkish forces a genocide. Ankara strongly denies that the killings a century ago amount to a genocide.

German Chancellor Angela Merkel is keen to stress common interests with Turkey as she presses to complete an EU-Turkey deal that would stem the flow of migrants to Europe in return for cash, visa-free travel rights for Turkish citizens and accelerated talks on Ankara's EU membership.

But she faces pressure at home to take a tougher stance against Turkey over its treatment of human rights activists and recent statements by Turkish President Tayyip Erdogan suggesting that German lawmakers of Turkish origin had "tainted blood".

A German court on Tuesday rejected an appeal by Erdogan after he was denied an injunction to prevent a German media executive from repeating an insulting poem about the Turkish leader.

(Reporting by Sabine Siebold; Writing by Andrea Shalal; Editing by Gareth Jones)