KNOWING YOUR ALLIES:

They are sworn enemies who insist they will never work together, but in practice, Hezbollah and the United States are already working -- separately -- on a common goal: to stop the extremist Islamic State from moving into Lebanon, where Hezbollah is the most powerful military and political player and currently shares with Washington an interest in stability.

Weeks after Hezbollah, the Shiite militant group and political party, helped repel an Islamic State attack on the town of Arsal on the Syrian border, new American weapons are flowing to help the Lebanese Army -- which coordinates with Hezbollah -- to secure the frontier. American intelligence shared with the army, according to Lebanese experts on Hezbollah, has helped the organization stop suicide attacks on its domain in southern Beirut.

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