Armed men broke into a United Nations outpost in a buffer zone separating Israel and Syria and abducted three UN military observers.
UN peacekeeping chief Herve Ladsous said that the unarmed observers were held by the Syrian men for about five hours and released unharmed on Wednesday morning.
It was the third abduction of UN peacekeepers in the tense region since March and underlined again their vulnerability in the spillover of the conflict in Syria, which is now in its third year.
Mr Ladsous called the latest abduction "a very serious incident ... that illustrates the very difficult conditions that now prevail" in and around the area separating Syrian and Israeli forces which is supposed to be free of armed groups.
The UN Security Council strongly condemned the abduction of the three observers by "a group of anti-government armed elements" who also looted the observation post.
Mr Ladsous, the under secretary-general for peacekeeping, did not say where the three military observers were from but the media in New Zealand reported that one was a New Zealander.
The first abduction - of 21 Filipino peacekeepers - on March 6 was by the Syrian rebel group, the Yarmouk Martyrs Brigade, which held them for three days.
Another group of four Filipino peacekeepers was abducted by the Yarmouk rebels on May 7 and released last Sunday.
The buffer zone between Syria and Israel had been largely quiet for four decades, but tensions have increased as the conflict in Syria has escalated.
Mr Ladsous reiterated that his department is doing contingency planning for a possible UN peacekeeping operation in Syria after the fighting ends.