Tens of thousands of Syrian refugees have poured into northern Iraq this week, after the Kurdish Regional Government that controls the area opened up a temporary bridge.

Previously, the U.N. Office of the High Commissioner for Refugees had registered 155,000 Syrian refugees in Iraq. The agency says the latest “exodus” is “among the largest we have so far seen during the conflict.”

In Jordan, where over half a million Syrian refugees are estimated to have fled, the economic and demographic effects of the crisis have strained the government’s ability to cope. In Iraq, the risks of instability are compounded by sectarian dynamics. Sunni extremists in Iraq and Syria are known to cooperate with each other.

Iraqi intelligence officials say the burgeoning cooperation is pumping new life into the Sunni insurgency in their country. They point to nearly 20 car bombings and suicide attacks that killed over 65 people, mostly in Baghdad, on the eve of the 10th anniversary of the U.S.-led invasion of Iraq last month.

On the Shiite side concerns have been raised that Iraqi Prime Minister Nouri Maliki is turning a blind eye to Iranian weapons shipments, and Iran-backed militias have for several years been described by U.S. military officials as the single gravest threat to Iraqi stability.

[Photo: FreedomHouse / Flickr]