The operations, which began six weeks ago, were approved by President Obama and involve several dozen troops from the U.S. military's clandestine Joint Special Operations Command.

A Yemeni official told the Associated Press Tuesday that the U.S. military and intelligence agencies have been participating in joint operations for some time with Yemeni troops, and the two countries are currently in discussions to build a new aviation unit to help bolster Yemen's counterterrorism forces.

Sources say that while the intelligence sharing has been critical, the Yemen military badly needs helicopters for its counterterrorism operations.

U.S. officials have said repeatedly that American advisers do not take part in raids in Yemen, but provide intelligence, surveillance, planning and other weapons assistance.