While leaders of the Syrian political and military opposition continue to deny any role for the extremists, Al Qaeda has helped to change the nature of the conflict, injecting the weapon they perfected in Iraq — suicide bombings — into the battle against President Bashar al-Assad with growing frequency. The evidence is mounting that Syria has become a magnet for Sunni extremists, including those operating under the banner of Al Qaeda. An important border crossing with Turkey that fell into Syrian rebels’ hands last week, Bab al-Hawa, has quickly become a jihadist congregating point.

The presence of jihadists in Syria has accelerated in recent days in part because of a convergence with the sectarian tensions across the country’s long border in Iraq. Al Qaeda, through an audio statement, has just made an undisguised bid to link its insurgency in Iraq with the revolution in Syria, depicting both as sectarian conflicts — Sunnis versus Shiite.

Iraqi officials said that the extremists operating in Syria are in many cases the very same militants striking across their country. “We are 100 percent sure from security coordination with Syrian authorities that the wanted names that we have are the same wanted names that the Syrian authorities have, especially within the last three months,” Izzat al-Shahbandar — a close aide to the Iraqi prime minister, Nuri Kamal al-Maliki — said in an interview Tuesday. “Al Qaeda that is operating in Iraq is the same as that which is operating in Syria,” he said.