Beirut (AFP) - Rebels including Al-Qaeda loyalists have seized most of the Syrian side of the armistice line with Israel on the Golan Heights, a monitoring group said on Saturday.

Al-Qaeda affiliate Al-Nusra Front and its allies launched a major offensive against government forces in Quneitra province last month, capturing the sole crossing point over the armistice line to the Israeli-occupied sector of the strategic plateau.

"The regime is on the retreat before the advancing rebels," Syrian Observatory for Human Rights director Rami Abdel Rahman told AFP.

"The regime has now lost control of about 80 percent of towns and villages in Quneitra province."

The rebels seized 45 UN peacekeepers on the Golan on August 28 and held them hostage until Thursday.

They are part of the 1,200-strong UN Disengagement Observer Force, which monitors a 1974 ceasefire between Israel and Syria on the Golan.

Israel seized 1,200 square kilometres (460 square miles) of the territory during the Six-Day War of 1967, then annexed it in 1981 in a move never recognised by the international community.

Syria has never relinquished its claim to the territory and its return was the subject of peace talks with Israel in the 1990s and again in 2008.

Any prospect of the the talks' resumption has been torpedoed by the uprising against President Bashar al-Assad's regime that erupted in March 2011 and swiftly escalated into a civil war that has claimed more than 191,000 lives.

The regime has lost control of much of the east to jihadists of the Islamic State group, including all of Raqa province and much of Deir Ezzor.

The air force carried out strikes on an IS training base in Deir Ezzor province on Saturday, killing eight of its militants, the Observatory said.

The Assad regime has stepped up its air campaign against IS in the east in recent weeks, but the near-daily strikes have exacted a heavy toll among civilians in militant-controlled towns.