Islamists of the al-Qaida-linked al-Nusra Brigade joined Syrian rebels today to seize a military air base near Aleppo, according to opposition fighters.
Videos posted online showed militants inspecting lines of large missiles.
A voiceover said they had captured the base after an overnight battle.
If true, it will increase fears that Islamist terror groups could get hold of devastating arms, including chemical weapons, as the country's bloody civil war rolls on, though Damascus insists its stockpiles are still safe.
But Qatari Foreign Minister Khalid Bin Mohammad al-Attiyah said that sending more arms to the rebels would prevent the emergence of "fanatics."
He called on the United Nations to "move quickly" to arm and fund rebel groups seeking to overthrow the Bashar al-Assad government.
"We should not leave it until a stage where, God forbid, somebody calls for jihad and we cannot stop people coming from all directions."
The Syrian government argues that this is already happening and that the revolt is dominated by foreign fighters.
The official Sana news agency reported fighting across the country, saying troops were clearing Aleppo's Karm al-Jabal suburb and had killed "dozens of mercenary terrorists."
But it did not comment on army casualties. Rebels said there was still fighting at Maarat al-Nuaman, a town between Aleppo to Homs which they seized from government forces earlier this week.
Turkey also scrambled jet fighters today when a Syrian helicopter bombed the town of Azmarin near the Turkish border.