The revelation that al Qaeda leader Ayman al-Zawahiri has been communicating directly with the group's Yemeni franchise about future operations is causing plenty of consternation among western counter-terrorism officials.

It suggests a heightened level of co-ordination between al Qaeda 'central' and its branches, and an initiative by Zawahiri to leverage instability in places far away from his hideout '" thought to be somewhere along the Pakistan-Afghan border.

There are still few confirmed specifics about the nature of the plot that Zawahiri was supposedly discussing with Nasir al-Wuhayshi, the leader of al Qaeda in the Arabian Peninsula (AQAP).

But he has clearly identified that group as an effective affiliate, possibly the one best placed to attack U.S. interests directly. U.S. officials were concerned that a plot was timed to go into operation to coincide with the end of Ramadan, which has often been a period of increased terrorist activity. The Muslim holy month ends on Wednesday.

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