The U.N. peacekeeping chief says armed men broke into a U.N. outpost in a buffer zone separating Israel and Syria early Wednesday and abducted three U.N military observers.

Herve Ladsous told a group of reporters Thursday that the unarmed observers were held for about five hours and released unharmed.

It was the third abduction of U.N. peacekeepers in the tense border region since March when 21 Filipino peacekeepers were held for three days by rebels fighting Syrian President Bashar Assad. Another group of four Filipino peacekeepers was abducted on May 7 by the same rebel group and released Sunday.

Ladsous called the latest abduction "a very serious incident" that illustrates the very difficult conditions in the area of separation, which is experiencing spillover from the Syrian conflict.