BEIRUT -- Three Syrian tanks entered the demilitarized zone in the Golan Heights on Saturday, Israel said, raising concerns violence from Syria's civil war could heat up a long-quiet frontier that has not seen such an incursion in nearly 40 years.
Israel complained to U.N. peacekeepers present in the area, a relatively low-key response that suggested it did not see the Syrian armor as an immediate threat. But the entry marks the most serious spillover of Syria's turmoil to date at the frontier, where stray ordnance has exploded on the Israeli side in the past.
Neighboring countries are dealing with a variety of incidents linked to the conflict -- Turkey exchanged artillery fire with Syria for a week last month, while Jordan has seen several shootings at the border and clashes linked to the uprising against President Bashar Assad have broken out in Lebanon.
Some in Israel worry that that if Assad goes, the country could fall into the hands of Islamic extremists or descend into sectarian warfare that would destabilizing the region. Islamic fighters -- some from abroad -- are increasingly taking part in key engagements alongside the rebels.
Inside Syria on Saturday for example, Islamic militants took part in a dawn assault on a strategic airbase in the north of the country. The attack, reported by activists, aimed to disrupt strikes by government warplanes and helicopters that are pounding rebel-held towns.
Anti-regime activist group The Syrian Observatory for Human Rights said the attack on the Taftanaz air base continued into the evening, although Syria's state-run SANA news agency said the fighting was over and government troops had repelled a "terrorist attack." The government considers the rebels terrorists and pawns in a foreign plot to destroy the country.
Fighters from Jabhat al-Nusra, an al-Qaida-inspired Islamic militant group made up of foreign jihadis, had joined in the assault, said the Observatory, which relies on reports from activists on the ground. Al-Nusra fighters, who are considered among the most experienced and disciplined among the forces fighting to topple Assad, have led attacks on other airbases in the north in recent months.
The Taftanaz base mainly houses military helicopters, near the main highway between the capital Damascus and the northern city of Aleppo -- where rebels and the military have been battling for control for months.
Online activist videos claim to show the battle, with rebels firing rockets and mortars, and smoke rising over buildings and an airstrip area. An activist speaking in the video identifies it as an attack by rebels and Jabhat al-Nusra on the base. The videos appear genuine and are consistent with other Associated Press reporting in the area.
Also on Saturday, war planes hit targets in the rebellious Damascus suburbs, killing at least 10 people and wounding dozens of others, the Observatory said. Fighter jets also bombed areas around the strategic northern city of Maaret al-Numan on a key supply route from Damascus to Aleppo, the country's commercial hub. Rebels have been using Maaret al-Numan as a base to disrupt government supplies to Aleppo.
The violence comes a day before the start of a key international conference in Qatar at which the United States and its allies aim to reorganize the opposition's political leadership and unite their ranks. The leadership-in-exile has been widely seen as ineffective and out of touch with rebel fighters on the ground.
Activists say more than 36,000 people have been killed during Syria's 19-month-old conflict, which began in March last year as a largely peaceful uprising but has transformed into a brutal civil war. Daily death tolls of 100 or more have become commonplace, and the country's sectarian divisions have deepened. Many of those trying to depose Assad are Sunni Muslims, while the regime is dominated by Alawites, followers of an offshoot of Shiite Islam.
On Friday alone, 125 people were killed in the fighting. At least 35 people were killed in the regime's artillery shelling of several towns in the oil-rich eastern province of Deir el-Zour, which borders Iraq, the Observatory said. At least 33 civilians were killed in the neighborhoods around Damascus, including several civilians who were shot by snipers, the group's president, Rami Abdul-Rahman said Saturday.
At least 48 soldiers were also killed in Friday's fighting, Abdul Rahman said. The government rarely comments on the deaths of soldiers, and there was no official confirmation of the particularly high toll among troops for the day.