A Syrian boy holds an AK-47 assault rifle in the majority-Kurdish Sheikh Maqsud district of the northern Syrian city of Aleppo, on April 14, 2013. In northern Syria, the Kurdish population has largely observed a careful compromise with regime and rebel forces, fighting alongside neither, in return for security and semi-autonomy over majority Kurdish areas, but there have been reports of Kurdish fighters joining the battle with Syrian rebels in certain areas, including in Sheikh Maqsud. #

In this image taken from video obtained from the Shaam News Network, which has been authenticated based on its contents and other AP reporting, smoke and fire rises after explosives were dropped by a Syrian government warplane in Yabroud near Damascus, Syria, on May 20, 2013. #

Rebel fighters from the Al-Ezz bin Abdul Salam Brigade attend a training session at an undisclosed location near the al-Turkman mountains, in Syria's northern Latakia province, on April 24, 2013. #

A Free Syrian Army fighter in a tunnel in Deir al-Zor, on April 6, 2013. The 30-meter (98-feet) tunnel was dug under an area where Syrian Army forces have set up base in Deir Al-Zor, according to members of the Free Syrian Army. #

This March 1, 2013 citizen journalism image provided by Aleppo Media Center AMC which has been authenticated based on its contents and other AP reporting, shows a Syrian child, injured by heavy bombing from military warplanes, in the town of Hanano in Aleppo, Syria. #

A Syrian soldier sits inside a tank as troops take control of the village of Western Dumayna, some seven kilometers north of the rebel-held city of Qusayr, on May 13, 2013. Syrian troops captured three villages in the strategic Qusayr area of Homs province, allowing them to cut supply lines to rebels inside Qusayr town, a military officer told AFP. #

Syrian troops celebrate as they take control of the village of Haydariyah, some seven kilometers outside the rebel-held city of Qusayr, on May 13, 2013. Syrian troops captured three villages in the strategic Qusayr area of Homs province, allowing them to cut supply lines to rebels inside Qusayr town, a military officer told AFP. #

Citizen journalism image provided by Aleppo Media Center AMC which has been authenticated based on its contents and other AP reporting, show flames rising from a car which was attacked by Syrian government forces, in Bustan al-Qaser neighborhood, Aleppo, on May 20, 2013. Fierce street fighting in the Syrian town near the Lebanese border killed at least 28 elite members of Lebanon's militant Hezbollah group, activists said, as Syrian government forces pushed deeper into the strategic, opposition-held town. #

An abandoned tank on a street near the minaret of the Omari mosque, which was damaged by what activists said was shelling by forces loyal to Bashar al-Assad, in Deraa, on April 13, 2013. #

A man works at a makeshift oil refinery site in al-Mansoura village in Raqqa's countryside, on May 5, 2013. Many civilians in the village who lost their jobs due to the Syrian conflict are making a living by refining crude oil to extract useful fuel such as gasoline and kerosene for sale. #

Mohammad, 11, a Syrian refugee boy who was injured during the conflict in Syria, sits in his wheelchair at a post-traumatic care center directed by Union of Syrian Medical Relief Organizations (UOSSM) in Hatay province, Turkey, on May 3, 2013. Turkey is now sheltering more than 300,000 Syrians who have fled the fighting in their homeland, most of them in camps along the 900-km (560-mile) frontier. #

In this undated file photo a Russian S-300 anti-aircraft missile system is on display in an undisclosed location in Russia. Russia's Deputy Foreign Minister Sergei Ryabkov said on May 28, 2013, that Moscow has a contract for the delivery of the S-300s to Syria and sees the deal as a key deterrent against foreign invasion in that country. The Deputy Foreign Minister wouldn't say whether Russia has shipped any of the long-range S-300 air defense missile systems, but added that Moscow is not going to abandon the deal despite strong Western and Israeli criticism. #

In this Tuesday March 19, 2013 file photo released by the Syrian official news agency SANA, a Syrian victim who suffered an alleged chemical attack at Khan al-Assal village according to SANA, receives treatment by doctors, at a hospital in Aleppo. The purported instances in which chemical weapons have been used in Syria have been relatively small in scale: nothing along the lines of Saddam Hussein's 1988 attack in Kurdish Iraq. That raises the question of who would stand to gain as President Bashar Assad's regime and the opposition trade blame for the alleged attacks and definitive proof remains elusive. #