The latest pledge by Al-Qaeda in the Arabian Peninsula to carry out more small-scale bomb attacks is being treated as a "very serious threat," the top US military officer said Sunday.

Responding to the Yemen-based terror group's vow to attack the West with small but frequent strikes such as last month's cargo plane parcel bombs, Admiral Mike Mullen gave credit to people who have so far foiled such plots but expressed concern over AQAP's persistence to break through.

"It's a very serious threat, and I believe what they are saying," the chairman of the US Joint Chiefs of Staff told ABC News show "This Week."

"They've grown, it's dangerous, and it's a place we need to focus," he added.

AQAP at the weekend unveiled what it described as its "strategy of a thousand cuts" that will "bleed the enemy to death", a monitoring group said.

The group said the packages it put aboard freight planes bound for the US in late October were never intended to cause mass casualties, but were aimed at creating maximum economic damage.

It said the parcels, which were intercepted in Dubai and Britain, were part of "Operation Hemorrhage," a plan that had cost just 4,200 dollars to mount.

When asked if AQAP's strategy worried him, Mullen responded "You bet it worries me."

But he stressed that there was "an awful lot of effort going on to make sure that they don't" succeed.

US Defense Secretary Robert Gates said last week that Washington wanted to help Yemen battle Al-Qaeda's affiliate in the country, and that providing equipment and training to Yemeni security forces offered the best way to counter the threat.

With more than 100,000 US troops fighting Al-Qaeda's allies in Afghanistan and public skepticism in Yemen over the US military's role there, Gates and other US officials have stressed that Sanaa will lead the fight against Islamist militants.