Renewed fighting between rebels and government forces is being reported in the Syrian Golan Heights, where 44 UN peacekeepers were abducted last week.
Activists said heavy clashes were raging around the Quneitra crossing, which rebels seized on Wednesday.
The whereabouts of the peacekeepers from Fiji is unclear, but it is thought they are being held by an al-Qaeda-affiliated rebel group, al-Nusra Front.
Al-Nusra says they are safe, and so far no demands appear to have been made.
Seventy-two Filipino peacekeepers were also surrounded in two different areas, but they managed to escape over the weekend.