Turkish authorities detained four people in an investigation into a potential threat against British and German diplomatic missions but found no links to any terrorist groups, the state-run Anadolu Agency said on Friday.
The investigation was prompted by intelligence about a potential Islamic State plot against the missions, Anadolu said.
Three of the suspects were detained in Ankara and one of them in Istanbul, it said.
Britain shut its embassy in the capital Ankara on Friday for what its foreign office said were security reasons, without giving further details.
The Germany embassy said on its website that its missions were only available for limited operations on Friday after a four-day public holiday this week.
Government offices and financial markets were closed in Turkey from Monday to Thursday for the Muslim Eid al-Adha holiday.
Turkey has suffered a series of suicide bombings and attacks by Islamic State and Kurdish militants over the past year. It launched its first major military incursion into Syria last month to push the jihadists away from its border and prevent Kurdish fighters from seizing territory as they retreated.
In its latest travel advice, Britain's foreign office urged against travel to within 10 km (6.2 miles) of the Syrian border and to Diyarbakir, the largest city in the mainly Kurdish southeast, hit by violence after a ceasefire with the outlawed Kurdistan Workers Party (PKK) broke down last year.