BEIRUT  - Syrian rebels on Sunday captured army checkpoints near Nayrab military airport in the northern city of Aleppo, in the eastern province of Deir Ezzor and in central Hama province, a watchdog said.

In Aleppo, fierce clashes took place between Syrian troops and several rebel battalions, which resulted in the insurgents taking over the checkpoint near Nayrab airport, the Syrian Observatory for Human Rights said. Nayrab is adjacent to Aleppo international airport, a key target for the rebels, who have also been battling troops guarding Kweyris military airbase east of the city and Menegh airbase to the north.

The Observatory, which collects its reports from a network of activists and medics in civilian and military hospitals on the ground, said at least six soldiers and a number of rebels were killed in Sunday's fighting.

Fighter planes carried out raids on rebel groups encircling the military defense factories in the town of Safireh east of Aleppo. In the eastern province of Deir Ezzor, rebels lost five men before capturing the Kibar checkpoint, seizing stores of weapons and ammunition and killing at least four soldiers, the watchdog said.

The districts of Sheikh Yassin and Hamidiyeh in the embattled city of Deir Ezzor came under army bombardment as warplanes circled overhead.

In the central province of Hama, the rebels lost one of their commanders when they took control of a military checkpoint near the town of Qalaa al-Maziq, where heavy regime shelling killed three people, including a child. The Observatory also reported that five soldiers were killed defending Tel Osman checkpoint before it fell to the insurgents.

East of Qalaa al-Maziq, regime forces stormed the town of Mork, which has seen several rounds of fighting, with advancing troops being pushed back by the rebels, and then entering again, the watchdog said. Mork is located on the highway connecting Hama to the strategic northwestern city of Maaret al-Numan, whose capture by the insurgents last October has hampered army supply lines to Aleppo further north. Regime forces are pushing to take back the strategic stretch of road.

The Observatory gave an initial toll of 42 people killed on Sunday in Syria, where the UN estimates that nearly 70,000 people have died since the outbreak of the uprising in March 2011.

Three Lebanese Shias were also killed in clashes in Syria, a Hezbollah official said on Sunday, as the opposition accused the group of fighting alongside its regime allies. "Two Lebanese Shias living in Syria were killed and at least 14 others wounded in clashes with rebels," the official told AFP on condition of anonymity, later adding that one of the wounded had also died.

Israeli Prime Minister Benjamin Netanyahu said Sunday that Israel will maintain close tabs on its border with Syria and only let people to cross in "exceptional circumstances," after seven injured Syrians were let in. "We will continue to watch over the border and prevent anyone from crossing it and entering Israel, except in a few isolated and exceptional circumstances -- each of which will be weighed on its own merit," Netanyahu told his outgoing cabinet.

Israeli troops in the occupied Golan Heights on Saturday allowed in seven people who were wounded in clashes on the Syrian side of the strategic plateau to cross the armistice line, taking them for treatment at a hospital in the northern town of Safed. All seven were taken to Ziv hospital where they were operated on, a spokeswoman told AFP. Netanyahu said the tensions along Israel's frontier with Syria would be a key element of his talks with US President Barack Obama when he makes his first visit to Israel as president next month.

On the political front, UN-Arab League peace envoy Lakhdar Brahimi urged international backing for a Syrian opposition offer to begin talks with the regime, which he proposed be held in United Nations offices. Brahimi said opposition leader Ahmed Moaz al-Khatib's offer to negotiate with some regime figures "opened the door and challenged the Syrian regime to confirm what it constantly says about being prepared to hold dialogue."

The envoy spoke at a news conference in Cairo after meeting Arab League chief Nabil al-Arabi.

"Parties in Syria, the Arab region and the international community must deal with this initiative for it to succeed," he said.

He added that holding talks "in one of the United Nations' headquarters between the opposition and an acceptable Syrian government delegation would be a start to exiting the dark tunnel."

Khatib is expected to visit Assad's backers in Moscow in the coming weeks, as is Assad's foreign minister Walid Muallem, though the two will not meet, according to Syrian state television.