BERLIN, July 20 (Reuters) - The German foreign ministry on Thursday warned its citizens to be more careful in traveling to Turkey, citing recent detentions of people there, and Ankara's refusal to grant consular access in some cases, in violation of international law.

"People who are traveling to Turkey for private or business reasons are urged to exercise increased caution, and should register with German consulates and the embassy, even for shorter visits," the ministry said in a revised travel guidance.

"Foreign ministry sites are not always informed in a timely manner about the detention of German citizens, and access for consular services is not always ensured," it added.

(Reporting by Andrea Shalal; Editing by Joseph Nasr) ((andrea.shalal@tr.com; +49 30 2888 5159; Reuters Messaging: berlin.newsroom@thomsonreuters.com;))