A Kosovan judge has ordered three Germans suspected of throwing an explosive device at the EU headquarters in Pristina to be held for 30 days.
The three reportedly deny involvement in the attack on 14 November, saying they were detained while investigating it themselves.
Windows in the glass-fronted building were shattered but nobody was hurt.
German and Kosovo media report that the men are German intelligence agents but officials in Berlin refuse to comment.
Lawyers for the detainees say the prosecution is seeking terrorism charges that carry a maximum 20-year sentence.
A spokesman for the German foreign ministry in Berlin confirmed that three Germans had been arrested on Thursday, but declined to make any further comment as an investigation was under way.
The German weekly Der Spiegel said the men worked for the German intelligence agency BND, and that they told investigators they had been examining the scene of the explosion, but had not been involved in it.
Kosovo declared independence from Serbia in February after nine years under UN stewardship and is recognised by more than 50 countries, including Germany.
Four days before the bomb attack, Kosovo’s Albanian majority rejected an agreement between the UN and Serbia on the deployment of the much-delayed EU police and justice mission Eulex.