Speaking after an EU–Western Balkans summit in Montenegro, Tusk said he had warned European partners weeks ago that such incidents could be expected, "sometimes intentional, sometimes not".
"We are dealing with events that will cause destabilisation. This requires great patience and caution," the Polish PM told reporters following talks with Romania's president on the sidelines of the gathering.
The Romanian defence ministry said the drone self-destructed and was of the type used in the war in Ukraine.
A search operation following the blast located three further unmanned vehicles in the area, the Reuters news agency reported.
European Commission President Ursula von der Leyen warned that Russia's war against Ukraine was "increasingly becoming a direct threat" to EU states on the bloc's eastern border.
She said Europe was investing in anti-drone capabilities, air defence and early-warning systems, and that the EU's SAFE rearmament programme would help build "a stronger Romania and a stronger Europe".
Security cooperation and resilience against hybrid threats were also on the agenda at the Montenegro summit.
(ał)
Source: PAP