BEIRUT (AP) -- A Syrian military helicopter crashed in a ball of fire Monday after apparently being hit during clashes between government forces and rebels in the capital Damascus, activists said, in a sign of the fighters' growing abilities as they struggle to topple President Bashar Assad's regime.

A video posted on the Internet showed the chopper engulfed in flames and spinning out of control shortly before it hit the ground amid bursts of gunfire near a mosque. Rebels shout "Allahu Akbar!" or God is great, as the helicopter went down. The authenticity of the video could not be independently verified.

In Paris, French President Francois Hollande ratcheted up the diplomatic pressure on the already isolated Assad regime, calling on the Syrian opposition to form a provisional government and saying France would recognize it once it was formed.

The announcement from Hollande -- believed to be the first of its kind --also appeared to be an attempt to jolt Syria's deeply fragmented opposition into unity. But Syria's fractured opposition has been rife with infighting since the anti-Assad revolt broke out in March 2011, and it is far from clear whether it could cobble together a provisional administration anytime soon.

"France asks the Syrian opposition to form a provisional government -- inclusive and representative -- that can become the legitimate representative of the new Syria," Hollande said in a speech to France's ambassadors. "France will recognize the provisional government of Syria once it is formed."

Syria's lightly armed rebels have grown bolder and their tactics more sophisticated in recent months. There have been claims of fighters shooting down helicopter gunships in the past, though the government has never confirmed it.

With its forces stretched thin by fighting on multiple fronts, Assad's regime has increasingly turned to air power, unleashing both helicopters and fighter jets on the rebels.

The Britain-based Syrian Observatory for Human Rights, which along with other activists reported the chopper crash, said there was intense fighting between troops backed by helicopter gunships and rebels in the western Damascus neighborhood of Jobar.

Syria's state-run news agency confirmed the crash in the district of al-Qaboun, which is near Jobar and a hotbed of Sunni Muslim rebels fighting to topple Assad. SANA gave no details about the cause of the crash in its one-line report, perhaps an implicit acknowledgement that it had been brought down by the rebels.

The opposition fighters are not known to have any answer to the regime's warplanes except anti-aircraft guns that they mostly use as an anti-personnel weapon. Last month, rebels claimed to have shot down a Russian-made MiG fighter, but the government blamed the crash on a technical malfunction.

The helicopter in the grainy video appeared to be a Russian-built Mi-8, or its similar but more powerful variant, the Mi-17. The easy-to-maintain, twin-turbine choppers are the most widely produced and exported helicopters in the world. The Mi-8, which can carry 24 troops, has been in Syrian air force service since the 1970s.

The military has for more than a month been fighting major battles against rebels in Damascus and its suburbs while engaged in what appears to be a stalemated fight in the north against rebels for control of Aleppo, the nation's largest city and commercial capital. The government has recently intensified its offensive to recapture districts in Damascus and its suburbs that have fallen into rebel hands.

Over the weekend, evidence mounted of mass killings by government forces in the Damascus suburb of Daraya.

Activists reported that regime forces went on a days-long killing spree after they seized Daraya from rebels Thursday. Reports of the death toll ranged from more than 300 to as many as 600. It was impossible to independently verify the numbers because of severe restrictions on media coverage of the conflict.

In Washington, State Department spokeswoman Victoria Nuland said more than 300 people were killed in fighting in the Damascus suburbs over the weekend, including 150 in one location.

She cited reports from human rights activists that some were killed point-blank "in the most brutal way at the hands of the regime" in Daraya. But she added that the U.S. reporting on the toll was also based on information from its own contacts inside Syria.

Despite the escalating violence, Nuland did not endorse France's call for the Syrian opposition to form a provisional government, saying "it's a matter for them (Syrians) to decide if and when they may be prepared to start naming folks."

The U.S. has called for Assad to step down, but so far has limited its support for the rebels to "non-lethal" assistance, meaning supplies and help that do not include ammunition or weapons.

In New York, U.N. Secretary-General Ban Ki-moon called for an immediate, independent investigation into the Daraya killings. U.N. spokesman Martin Nesirky also said the killings underscore the urgent need to move "from bloodshed to political dialogue" and the need to hold those responsible for "atrocities" accountable.

Video posted on the Internet by activists showed rows of bodies, many of them men with gunshot wounds to the head. During mass burials on Sunday, bodies were sprayed with water from hoses -- a substitute for the ritual washing prescribed by Islam in the face of so many dead. The gruesome images appeared to expose the lengths to which Assad's authoritarian regime was willing to go to put down the rebellion that broke out in March last year.

In the north, thousands of Syrians fleeing violence were stuck at the border with Turkey after Turkish authorities blocked access to any more refugees while they rushed to build more camps to accommodate the deluge.

The refugee crisis is just one of many examples of how the civil war is spilling across borders into neighboring countries such as Turkey, Lebanon and Jordan -- all of which have seen a massive influx of Syrians.

A Turkish official said the refugees still stuck on the Syrian side will be allowed in "within a day or two" when a new camp near the border is ready. Another official said Turkey also was carrying out more stringent security checks on the refugees, adding to the delays in crossing.

Turkey fears that Kurdish rebels fighting for self-rule in southeast Turkey may be coming in through Syria. There are also concerns that foreign jihadists are moving in and out of Turkey to fight the Syrian regime. The officials spoke on condition of anonymity because there were not authorized to brief the media.

The official Syrian News Agency, SANA, also reported that authorities released 378 people detained for participation in peaceful street protests. It said those freed were never involved in acts of violence, an indirect admission that scores of people were detained for simply taking part in peaceful anti-government protests.

Authorities have issued similar pardons in the past, a practice apparently designed to isolate the rebels and create the image of a compassionate regime.

Vice President Farouk al-Sharaa said Syria approved of an initiative Iran plans to present at a world gathering of nonaligned nations in Tehran later this week. Iran says it plans talks on a peace plan to end Syria's civil war, but hasn't provided any details.

Any Iranian initiative proposing dialogue between the government and the opposition would likely be a nonstarter because rebels refuse to talk to Assad and because of Tehran's close bonds with his regime.

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AP writers Jamey Keaten in Paris, Suzan Fraser in Ankara, Turkey, Matthew Pennington in Washington, and Slobadan Lekic in Brussels contributed to this report.