Syria conflict: Fresh clashes erupt in Golan Heights
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.
Persistent gunfire and explosions could be heard from the Israeli-occupied Golan on Monday as Syrian rebels and government forces battled for controlled of the Quneitra crossing and the village of Hamidiya.
The Reuters news agency reported that at least one Syrian army tank was involved and that rebels were moving with a few metres of a fence marking the 1974 ceasefire line.
The head of the UK-based Syrian Observatory for Human Rights, Sami Abdul Rahman, said al-Nusra appeared to want to "end once and for all the regime's presence in the area" and also to "expel the international observers".
Earlier, UN Secretary General Ban Ki-moon again demanded the immediate and unconditional release of the Fijian peacekeepers serving with the UN Disengagement Observer Force (Undof) seized on Thursday.
Al-Nusra published on Sunday photographs of what it said were the seized peacekeepers, along with their identification cards. It said they were "in a safe place and in good health".
The jihadist group said they were seized because the UN was "ignoring the daily shedding of Muslims' blood in Syria" and co-operating with government forces to "facilitate its movement to strike the vulnerable Muslims" in the demilitarised zone.
The targeting of Undof has led to criticism from contributing nations.
The Republic of Ireland warned it would not send replacements for its 130-member armoured rapid response unit next month if Undof's firepower, command and control, and rules of engagement were not strengthened.
"I've made it very clear that I'm not going to continue to commit Irish troops to this mission unless there's a very fundamental review of how it's going to operate. Clearly this is no longer a demilitarized zone," Irish Defence Minister Simon Coveney told RTE radio.
This is not the first time Undof personnel have been detained by rebel fighters in recent years. Peacekeepers were detained in March and May of 2013 and were released safely.
Israel seized most of the Golan Heights in the closing stages of the 1967 Six-Day War, and thwarted a Syrian attempt to retake it in 1973. Both countries signed an armistice in 1974, after which Undof was put in place to monitor the demilitarised zone.