The German embassy in Ankara was shut Thursday along with the consulate general and a German school in Istanbul, following a terrorism warning days after a bombing in the capital Ankara.
The Istanbul consulate said in an email to German citizens that the closures were made after a warning that was "not conclusively verifiable."
Both facilities would stay shut on Thursday as a precaution, the email said.
Germany's foreign office issued a statement on its website urging anyone in Istanbul, Ankara or other major cities in Turkey to be on high alert.
The warning advised against congregating in large groups in public spaces; visiting tourist attractions; and spending time in areas near government or military facilities.
The German consulate general in Istanbul is located not far from the city's bustling Taksim Square.
At least 37 people were killed in a car bombing in Ankara on Sunday, which was claimed by the hardline Kurdistan Freedom Falcons (TAK).
TAK is a splinter group of the banned Kurdistan Workers' Party (PKK), with whom Turkey has fought a bloody war since a two-year ceasefire broke down in July 2015.
In January, 12 German tourists were killed in a suicide attack in central Istanbul blamed on the Islamic State militant group.
Thursday's closures in Istanbul came two days after the German embassy warned its citizens of potential further attacks in the Turkish capital.