BERLIN (Reuters) - German lawmakers, rights activists and celebrities said on Monday they had filed a civil suit against Turkish President Tayyip Erdogan and some of his aides for what they called "war crimes" in counter-terrorism operations against Kurdish militants.

Turkish-German relations have been deteriorating lately over a resolution passed by the German parliament declaring the 1915 massacre of Armenians by Ottoman forces a genocide.

Chancellor Angela Merkel now faces mounting domestic pressure to hold Erdogan accountable for human rights abuses after last year's collapse of a ceasefire between Ankara and PKK militants seeking autonomy in Turkey's main Kurdish southeast. Thousands have been killed in the renewed conflict.

"Our clients consider it an ethical obligation to bring charges for systematic war crimes in Turkey here in the Federal Republic as is possible according to the Code on International Criminal Law," lawyers Britta Eder and Petra Dervishaj said in the complaint filed with the Federal Prosecutor.

A spokeswoman for the prosecutor said she could not confirm that the complaint had been filed.

The complaint also targets former Turkish prime minister Ahmet Davutoglu and various other Turkish politicians and members of the government, military and police.

Among those behind the court action were German songwriter Konstantin Wecker, actor Rolf Becker, numerous lawyers and human rights representatives as well as lawmakers from the opposition Left Party.

Left Party lawmaker Ulla Jelpke said Erdogan needed to face pressure at a time when the German government was loath to criticize the Turkish president for fear of jeopardizing an EU deal to stem the flow of migrants out of Turkey to Europe.

The main aim of the complaint was to raise public awareness about crimes against Turkey's minority Kurds, she added.

(Reporting by Caroline Copley; Editing by Mark Heinrich)